Fabrication and study of SnO2 - scbaghdad.edu.iqscbaghdad.edu.iq/library/Physics/MS.C/2014/Fabrication and study.pdfDedication ﺎﻴﻧﺪﻟﺍ ﻦﻋ ﻞﺣﺭ ﻦﻣ ﻰﻟﺍ

Republic of Iraq

Ministry of Higher Education

and Scientific Research

University of Baghdad

College of Science

Fabrication and study of SnOR2R UV-Photodetector

A Thesis

Submitted to the Comittee of College of Science, University of Baghdad

in partial Fulfillment of the Requirements for the Degree of

Master of Science in Physics

By

Azhar Shaker Norry (B.Sc. in Physics 1994)

Supervised by

Prof. Dr. Abdulla M. Suhail

LLeett.. DDrr.. Asama N. Naje

2014 AD 1435 AH

بسم هللا الرحمن الرحيم

وح ويسألونك وح قل الر عن الر

من أمر ربي وما أوتيتم من

العلم إال قليال

صدق هللا العظيم

سورة األسراء

۸٥األية

Supervisor Certification

we certify that this thesis was prepared by Miss Azhar Shaker Norry under my supervision at the Physics Department/College of Science/University of Baghdad in a partial requirement for the degree of Master in Physics Science in nanotechnology and optoelectronics.

Prof. Dr. Abdulla M. Suhail

Physics Department

College of Science

University of Baghdad.

/ / 2014

Dr. Asama N. Naje

Physics Department

College of Science

University of Baghdad.

/ / 2014

In view of the available recommendations, I forward this thesis for debate by the examination committee

Prof. Dr. Raad M. S. Al-Haddad

Chairman of the Physics Department

College of Science, University of Baghdad.

/ / 2014

Certification This is to certify that we have read this thesis entitled: " Fabrication and study of SnO2 UV-Photodetector " as an examine committee, examined the student Azhar Shaker Norry in its contents and that, in our opinion meets standard of a thesis for the Degree of Master of Science in Physics. Signature: Name : Shatha M.AL-Hilly Title : Asst. Prof. Address : University of Baghdad Date : / /2014 (Chairman) Signature: Name : Amel Kadhim Jassim Title : Asst. Prof. Address : University of Baghdad Date : / /2014

(Member)

Signature: Name : Alwan M.Alwan Title : Asst. Prof. Address : Technalogy University Date : / /2014

(Member)

Signature: Name : Asama N. Naje Title : Asst. Prof. Address : University of Baghdad Date : / /2014 (Supervisor)

Signature: Name : Abdulla M. Suhail Title : Prof. Address : University of Baghdad Date : / /2014 (Supervisor)

Approved by the Council of College of Science.

Signature : The Dean : Asst.Prof. Mohammed A.Atiya

Address : The Dean of Collage of Science, University of Baghdad Date : / /2014

DDeeddiiccaattiioonn

الى من رحل عن الدنيا

بفضله ولم يرى ثمار العمر كيف تزهو

الى المرحوم (ابى العزيز)

الى من ارضعتني الحب والحنان

الى رمز الحب وبلسم الشفاء

الى القلب الناصع بالبياض (امي العزيزة)

الى من احمل اسمه بكل فخر

الى سندي وقوتي ومالذي بعدهللا

الى من آثرني على نفسه

الى من اظهر لي ماهو اجمل من الحياة (زوجي الحبيب)

الى من اعطوني القوة

الى من اعطو لحياتي معنى

الى من وقفوا معي دوما (اخوتي)

الى من يعطيني الصبر في الحياة

الى نور عيني و فلذات كبدي (اوالدي)

اأهدي لكم ثمرة جهدي المتواضع هذ

Acknowledgment

Thanks to God who helped me to accomplish this work which I

hope will serve our community.

I would like to express my deep gratitude and appreciation to my supervisors Dr. Abdulla M. Suhail and Dr. Asama N. Naje for suggesting the topic of the thesis, continuous advice and their guidance through this work.

I am grateful to the Dean of the College of Science and the staff of Physics Department for their valuable support and for making all facilities necessary for the research available.

My thanks are extended to the staff of the photonics and nanotechnology Group, especially Mr.Omer and Dr.Qahtan G. Al-zaidi .

My deepest appreciations are expressed to staff of the Ministry of Science and Technology/ Department of Materials Chemistry especially to the X-ray Diffraction staff for their help in the measurements of structural and optical properties of samples .

I would like to thank Dr. Kadhem A.Adem Dr. Issam M. Ibrahim and to the thin film group for their contribution in this study.

Finally, I would like to thank my family for their support

and patience.

AzhAr

LLiisstt ooff SSyymmbboollss aanndd AAbbbbrreevviiaattiioonnss

Description Symbol Atomic Force Microscopy AFM Aluminum Al Bohr radius aRB lattice parameters a,b,c Crystalline Silicon C- Si

Conduction band C.B Speed of light c Detectivity D Specific Detectivity D* Energy band gap ERg activation energy ERiR Optical energy gap opt

gΕ Electronic excitation energy in electron volts ERexc electron charge e Electron Volt eV Fourier transform infrared spectroscopy FTIR Face Centered Cubic

FCC Photocurrent Gain G Hydro Furan Acid HF Miller indices hkl Planck’s constant h Photon energy hυ photocurrent IRph Noise in Detectors IRn Current-Voltage I-V Wave vector k Noise Equivalent Power NEP

Molarity M electron concentration n Porous silicon

PS

photoconductive PC photovoltaic PV Photoluminescence Spectrum PL hole concentration P p-Type of semiconductor material p-type Quantum Well Q.W quantum wire Q .wire Quantum Dot Q.Dot the detector resistance RRd Responsivity RRλ root mean square r.m.s Scanning Probe Microscope SPM Silicon Si transmission electron microscopy TEM Tetra Hydro Furan THF transit time TRr Ultraviolet UV Visible VIS Valence band V.B Bias voltage (applied voltage) VRB load voltage VRL X-ray diffraction XRD resistivity ρ Diffraction angle(degree) Ɵ Ohme Ω conductivity σ carrier lifetime τ

majority carrier mobility μ Hole mobility µRh electron mobility µRe quantum efficiency η internal quantum efficiency ηRo wavelength λ Maximum wavelength (cut off wavelength) λRC Fermi wavelength λRF free space wave length λR° Watt (unit for measuring the power ) W

Abstract

In this work a Tin Oxide (SnO2) UV photoconductive detector was fabricated. The Tin Oxide nanopowder is prepared by chemical method and deposited on glass and porous silicon by dipping coating technique. The structural , morphological, optical and electrical properties of the prepared SnO2 nanopowder are studied . The structure of the nano powder are examined by X-ray diffraction (XRD) and found to be polycrystalline of tetragonal structure with strong crystalline orientation at (110 and 101).The optical energy gap is calculated by the absorption spectrum which gives a value of 3.78eVand 4.3eV. The photoluminescence emission spectra of SnO2 nanoparticles at 280nm excitation, exhibit emission at 437nm. The emission maximum of 437 nm is lower than the band gap of the SnO2 bulk. The surface morphological studies demonstrate that SnO2 nanopowder deposited on PS is improved and the average particle size has determined from Scanning Probe Microscope, is about 73.65 nm. The Hall measurements show that the nanopowder prepared in such conditions are n-type with carrier concentration (n) of a bout -1.273×1017 cm-3. The I-V characteristics ( photoresponsivity , photocurrent gain and the normalized detectivity) of the fabricated detector are measured. The performance of the fabricated detectors are taken under illumination of the SnO2 detector using light power 2.5mW and 385nm UV radiation. The surface functionalization of the SnO2 deposited on porous silicon (PS) layer by polyamide nylon polymer has improved the photoresponsivity of the detector to 0.1 A/W. The response time of fabricated detector was measured by illuminating the sample with UV radiation and its values was (0.052ms). The normalized detectivity (D*) of the fabricated SnO2 UV detector at wavelength of 385 nm is found to be 1.8 ×1010 cm Hz1/2 W-1.

List of Contents

Contents Page

Chapter One: Introduction and Basic concepts 1.1 Introduction 1

1.2. Types of nano materials P

3

1.2.1 One – Dimension Confinement (Quantum Well) (Q.W)

3

1.2.2 Two – dimension confinement (quantum wire) (q.wire)

5

1.2.3 Three – Dimension Confinement (Quantum Dot) (Q.Dot)

5

1.3 Tin oxid SnO2

6

1.4 structure of SnOR2

6

1.5 properties of SnOR2

7

1.6 Application of SnOR2

7

1.7 Crystalline Silicon 8

1.8 Silicon structure

8

1.9 silicon properties

9

1.10 Porous silicon (PS) 10

1.11 Preparation Techniques

10

1.11.1 The Etching Process

10

1.11.2 Photochemical Etching Mechanism

11

1.12 Types of Optical Detectors

13

1.12.1 Thermal detectors

14

1.12.2 Photon detectors

14

1.13 Photoconductive Detectors

16

1.14 The Figure of Merit

19

1.14.1 Responsivity ( RRλ R)

19

1.14.2 Photocurrent Gain (G)

19

1.14.3 The Noise in Detectors (IRnR)

20

1.14.4 Noise Equivalent Power ( NEP)

20

1.14.5 Detectivity ( D ) and Specific Detectivity ( D* ) 21 1.15 The mathematical model of the photoconductive detector

21

1.16 Literature Survey

26

1.17 Aim of the work

30

Chapter Two: The Experimental Work 2.1 Introduction

31

2.2 Silicon wafer properties

31

2.3 Sample Preparation

32

2.3.1 Preparation porous silicon layer by photochemical etching 32

2.4 Preparation of SnO2 nanopowder by Sol gel method 34

2.5 Fabrication of Sno2/PS photoconductive detector

34

2.5.1 Preparing the solution 34

2.5.2 The mask

35

2.6 Fabrication of SnO2/PS photoconductive( UV) detector coated

with a polymer

36

2.6.1 Chemical material:

36

2.6.2 Coating of the SnO2 films/PS by the polymer

36

2.7 Atomic Force Microscopy (AFM)

37

2.8 Structre Measurements 38

2.8.1 X-Ray Diffraction studies 38

2.8.2 Optical Properties

39

2.8.2.1 UV – VIS absorption spectrum

39

2.8.2.2 Photoluminescence Spectrum (PL)

40

2.9 Electrical Properties of the detector

40

2.9.1 Hall Effect Measurement

40

2.9.2 Detector Characteristic Measurement

41

Chapter Three:Results and discaussion 3.1 Introduction

43

3.2 Structure Properties

43

3.2.1 X-ray diffraction results of SnO2 film

43

3.2.2 Atomic Force Microscopy

44

3.3 Optical Properties

47

3.3.1 UV-VIS absorption Spectrum

47

3.3.2 The energy band gap calculation 48

3.3.3 The optical Photoluminescence spectrum

49

3.4 Hall Measurements 50

3.5 The Photodetector Measurements

50

3.5.1 I-V Characteristics

50

3.5.2 The Specific Detectivity ( D*) 53


53

3.5.4 The Response Time

54

3.6 Conclusion

55

3.7 Suggestions of future work

55

References

List OF Tables

List OF Figures

Table Table Caption Page

(1-1) properties of SnOR2R wurtzite structure 7

(3-1) Hall effect parameters for SnOR2R film deposited on porous silicon

50

Figure Figure Capton Page

(1-1) Types of electron confinement 3

(1-2) Density of states as a function of energy for bulk material, quantum well, quantum wire and quantum dot

4

(1-3) Quantum films(multiple quantum wells superlatices)(1-D quantization)

4

(1-4) structure of SnO2 6


(1-5) Diagram of the reaction mechanism for PS formation

13

(1.6) Relative spectral response for a photo detector and a thermal detector

14

(1-7) photoconductive detector

16

( 1-8) Processes of photoconductive for semiconductor 18

(1-9) The operation circuit diagram of SnOR2R photoconductive detector where; RRdR is the detector element, RRL Ris the load resistance and VRCR is the bias voltage

23

(2-1) The set up of the photochemical etching process ,(photograph of the system)

33

(2-2) (a) Schematic diagram of interdigital electrodes,(b) Photographic plate of photoconductive mask

35

( 2-3) Scanning probe Microscope( Type AA3000) AFM 37

(2- 4) SHIMADZU XRD-6000 X-ray diffractometer (CuKRα Rradiation λ=0.154 nm )

38

( 2-5) Schematic Mask for the Hall effect measurement 40

( 2-6) Schematic diagram of the experimental setup 42

(3-1) XRD pattern of the SnOR2R nanoparticles 44

1T (3-2a) 1T2D×3D Scanning prob microscope image of porous silicon layer of 10 min etching time

45

1T (3-2b) 1TSPM image of SnO2 on PS with etching time 10 min

46

(3-3) 0TThe absorption spectrum of SnOR2 47


(3- 4) Plot of 1T(αhυ)P

2 P1T vs. photon energy (hυ) for SnO R2 48

(3-5) (αhυ)P

2P versus Photon energy for SnO2 thin film 49

( 3-6 ) The variation of the photocurrent of the fabricated SnOR2R UV detector on porous silicon layer as a function of the bias voltage at etching time 10min

51

( 3-7 ) The variation of the photocurrent of the fabricated s

52

(3- 8 ) The photoresponse time of fabricated SnOR2R UV detector1T.The time base on x-axis is 500 μs/div

54

Chapter One

Introduction and Basic Concept

۱

Chapter One Introduction and Basic Concept

1.1 Introduction

Nanotechnology In the last decades, a little word attracted

enormous attention, interest and investigation from all over the world:

“nano”. What it presents in terms of science and technology, which are

also called nanoscience and nanotechnology, is much, much more than

just a word describing a specific length scale. It has dramatically changed

every aspect of the way that we think in science and technology and will

definitely bring more and more surprises into our daily life as well as into

the world in the future.

The classical laws of physics and chemistry do not readily apply at

nano very small scale for two reasons Firstly, the electronic properties of

very small particles can be very different from their larger cousins.

Secondly, the ratio of surface area to volume becomes much higher, and

since the surface atoms are generally most reactive, the properties of a

material change in unexpected ways[1].

Nanoparticles are usually defined as particles less than 100 nm in

diameter[2] . Due to their large surface area to volume ratio, nanoparticles

may have unusual and unique properties not attributed to larger

particles,and are often be more reactive[3,4,5].

Due to the small particle size, the surface area of the nanomaterials is

much larger than that of bulk materials, leading to a large fraction of

surface atoms, large surface energy and reduced imperfections.

Moreover, the nanoparticles can be assembled into various nanostructures

and microstructures. These features give unique electrical, chemical,

optical, and mechanical properties to nanomaterials, which would inspire

the creation and fabrication of new devices and the invention of new

technologies, here is an example of how the interfacial characteristics

۲


affect the device applications. Nanomaterials have a significantly lower

melting point than bulk materials, due to a large fraction atoms in the

total amount of atoms [6].

There are two principal ways of manufacturing nanoscale materials; the

top-down nanofabrication starts with a large structure and proceeds to

make it smaller through successive cuttings while the bottom-up

nanofabrication starts with individual atoms and builds them up to a

nanostructure[7].

Several methods have been studied in fabricating these nanostructures,

which include laser ablationP

P, chemical vapor deposition (CVD) and

template-directed growth. In order to integrate one dimensional

nanomaterial into a device, a fabrication method that enables well-

ordered nanomaterials with uniform diameter and length is important.

Template-directed growth is a nanomaterials fabrication method that uses

a template which has nanopores with uniform diameter and length . Using

chemical solutions or electro deposition, nanomaterials are filled into the

nanopores of the templates and, by etching the template, nanowires or

nanotubes with similar diameter and length as the template nanopores are

obtained. Because the size and shape of the nanomaterial depends on the

nanoholes of the template, fabricating a template with uniform pore

diameters is very important. Nanomaterials can be classified by different

approaches such as; according to the X, Y and Z dimensions, according to

their shape and composition. The more classification using is the

order of dimension into 0D (quantum dot), 1D (nanotube, nanowire and

nanorod), 2D (nanofilm), and 3D dimensions such as bulk material

composited by nanoparticles[8].

۳


1.2. Types of nano materials P

Nanostructure is divided into three classes as shown in figure (1-1)P

1. One-dimension confinement (quantum well)

2. Two-dimensions confinement (quantum wire)P

3. ThreeP

P-dimensions confinement (quantum dot)[9,10]

Bulk Quantum Well Quantum Wire Quantum Dot

Figure(1-1): Types of electron confinementP

[11]

1.2.1 One – Dimension Confinement (Quantum Well) (Q.W) A quantum well is a potential well that confines particles, which

were originally free to move in three dimensions, in two dimensions,

forcing them to occupy a planar region. Their motions are confined in the

direction perpendicular to the free plane. The effects of quantum

confinement take place when the quantum well thickness becomes

comparable at the de Broglie wavelength of the carriers (generally

electrons and holes), leading to energy levels called "energy subbands",

i.e., the carriers can only have discrete energy values, as in the fig (1-2).

In quantum well the electron are free in Z and Y directions, whereas it is

٤


confined in the X direction. When λRFR>LRxR and LRxR <<LRyR , LRzR where λRFR

represent the Fermi wavelength.

Figure(1-2): Density of states as a function of energy for bulk material, quantum well,

quantum wire and quantum dot [12].

Quantum wells are formed in semiconductors by having a

material, like gallium arsenide sandwiched between two layers of a

material with a wider bandgap, like aluminium arsenide. These structures

can be grown by molecular beam epitaxy or chemical vapor deposition

with control of the layer thickness down to monolayers as shown in fig

(1- 3). This is now common in industry, in research, and even for

academic students[13].

Figure (1-3):Quantum films(multiple quantum wells superlatices)(1-D

quantization)[14] .

٥


1.2.2 Two – dimension confinement (quantum wire) (q.wire) In this configuration the electron motion is confined in two

directions and allowed only along the wire axis, as shown in fig (1-1) The

coulomb potential is .

x

exVε

2

)( −= ……………1-1 ;Ɛǀxǀ:electrical filed

The attraction force between the electron and hole in quantum wire

is stronger than in bulk or in the quantum well[15]. 1.2.3 Three – Dimensions Confinement (Quantum Dot)

(Q.Dot) In this system the carriers are confined in all directions, in quantum

box or quantum dotP

P. as in fig(1-1). Depending on the ratio of

confinement length (d) to the Bohr radius (d/aRBR) of the exciton in bulk,

there are two distinct regimes, namely:

The exciton confinement regime and charge carries confinement

regime.

when 1⟩⟩Bad the motion of exciton is not confined due to boundary

conditions. when 1⟨⟨Ba

d , The number of excitons or of bound states is

formed because the kinetic energies of the electron and the hole are larger

than the Coloumb energy . The wave function is squeezed due to strong

confinement and the electron, and the hole individually occupy the lowest

energy state in a confined potentialP

P. The dimension of a quantum dot is

smaller than the De Broglie wavelength of thermal electrons, which is

( ) ( )nm

kTm

h

Em

hh

ee

6.722 2

121 ===

Ρ=λ ……..1-2

An important property of a quantum dot is its large surface to

volume ratio. The consequence of this feature is that quantum dots have

pronounced surface-related phenomena [16].P

٦


1.3 Tin Oxide SnOR2 R

Tin oxid is an n-type semiconducting metal oxid with awide bandgap

(3.6eV)at 300 K [17,18] . wave – length more then 0.4 µm[19]. is typically

n-type. Because of its high quality of electrical [20],optical (transparent for

visible light and reflective for IR and electrical properties, allied to good

chemical and mechanical stability [21] .

Tin (Sn) is a naturally occurring element that appears in group 14

(4A) of the periodic table. Tin is a silver-white metal that is malleable and

somewhat ductile [22] .

1.4 Structure of SnOR2

Tin oxide has a tetragonal rutile [23] crystalline structure known in

its mineral form as (cassiterite) with point group14 4h D and space group

P42/mnm. The unit cell consists of two metal atoms and four oxygen

atoms. Each metal atom is situated in a midst six oxygen atoms which

approximately.

The lattice parameters of SnO2 are, a =b= 4.7382 Å and c = 3.1871

Å[24,25].

Fig (1-4): structure of SnOR2R [26,27].

http://www.google.iq/url?sa=i&source=images&cd=&cad=rja&docid=1OQ5GF5R3uNsTM&tbnid=CPutmrknsW2sKM:&ved=0CAgQjRwwAA&url=http://www.springerimages.com/Images/RSS/1-10.1007_978-0-387-68318-8_14-0&ei=-tARUsGEO-rl4QTj2IH4DQ&psig=AFQjCNHNzflMaxltKNUicrGVcGxpZ7-E2g&ust=1376985723019885

۷


1.5 properties of SnOR2 Nature of the properties of the SnO2 crystals depend on different

kind of defects and impurities that are present in the structure of this

material. These defects could affect its structural, electronic, optical

and/or magnetic properties[28]. Table(1-1):Physical properties of SnOR2R wurtzite structure [29].

Properties

1TUMolecular formulaU1T SnOR2

lattice parameters a =b= 4.7382 Å , c = 3.1871 Å

1TUMolar mass U1T 150.709 g/mol

Eenergy gap 3.6 eV

Thermal conductivity 0.98 WKP

-1P cmP

-1P at room temperature

Appearance white powder

1TUDensityU1T 6.95 g/cmP

3

1TUMelting pointU1T 1800–1900 °C (sublimes)

1TUBoiling pointU1T 2073°F

1TUSolubilityU0T1T 0Tin1TUwaterU1T Insoluble

1TURefractive indexU1T(n) 2.006 1.6 Application of SnOR2

Research on tin dioxide (SnOR2R) attracts a lot of interest because it

has been widely used in many applications, such as transparent electrodes

[30], far-infrared detectors, and high-efficiency solar cells (200), gas

sensors [31,32],solid state chemical [33], solid state gas sensing material

surface [34], electrocatalytic electrodes [35], Liguid crystal displays ,

optoelectronic devices , heat reflecting mirrors[36] , capacitors[37],

lithium-ion batteries [38].

http://en.wikipedia.org/wiki/Chemical_formula

http://en.wikipedia.org/wiki/Molar_mass

http://en.wikipedia.org/wiki/Density

http://en.wikipedia.org/wiki/Melting_point

http://en.wikipedia.org/wiki/Boiling_point

http://en.wikipedia.org/wiki/Solubility

http://en.wikipedia.org/wiki/Water

http://en.wikipedia.org/wiki/Refractive_index

۸


1.7 Crystalline Silicon

Crystalline Silicon (C- Si ) has a relatively small and indirect band

gap of approximately 1.12 eV . Moreover , highly pure C- Si has a small

exciton binding energy of ~14meV . Silicon is the most prevalent

semiconductor used in microelectronics and photonics; it is produced in

higher volume for lower cost than any other semiconductor. The band gap

of silicon leads to efficient detection of visible light and conversion of

sunlight into electricity. Easily integrated with other microelectronics,

silicon is used in many forms including (crystalline, amorphous, and

porous) in numerous optoelectronic devices. Optical quality silicon is

highly transparent in the far – infrared region and opaque in the visible

and ultraviolet region P

P. Silicon surface has high absorbtivity for oxygen

and the growth rate of oxide layer on silicon surface is nearly (2nm/min)

under ambient condition. This oxide layer has a considerable effect on the

absorbity of the surface for photons of energies higher than 6eV.

Reducing dimensionality of bulk silicon to nano-scale silicon

(Porous silicon) leads to appreciable change in optical , electrical and

electronic properties[39].

1.8 Silicon structure Silicon is the most common metalloid , one of only a very few

elements that have characteristics of both metals and non-metals. It is a

semiconductor material, which has the symbol Si and atomic number 14.

Silicon is the eighth most common element in the nature by mass, but

very rarely occurs as the pure free element in nature. It is more widely

distributed in dusts, sands, planetoids and planets as various forms of

silicon dioxide (silica) or silicates. Silicon, like carbon and germanium,

crystallizes in a diamond cubic crystal structure. The lattice spacing for

۹


silicon is 0.5430710 nm. Silicon lattice has a diamond-like structure and

it consists of two interpenetrating FCC lattice, silicon is also part of the

the carbon family.

When considering silicon as a material for optoelectronic applications,

device for which conventional silicon technology falls short is the

light emitter, since crystalline silicon is an inefficient light - emitting

material. Because silicon is an indirect band gap material (1.12 eV) which

leads to low optical efficiency.

1.9 Silicon properties

Silicon is a metalloid, an element with properties of both metals and

non-metals. The melting point of silicon is 1410°C and the boiling point

is 2355°C. Its density is 2.33 g/cmP

3P. Silicon is a semiconductor, A

semiconductor is a substance that conducts an electric current better than

a non-conductor—like glass or rubber—but not as a conductor—like

copper or aluminum Silicon is a relatively inactive element at room

temperature. It does not combine with oxygen or most other elements.

Water, steam, and most acids have very little affect on the element. At

higher temperatures, however, silicon becomes much more reactive. In

the molten (melted) state, for example, it combines with oxygen,

nitrogen, sulfur, phosphorus, and other Porous Silicon material is a

network consisting of pores elements separated by thin columns and

contains nano-meter sized silicon crystallites, as a result, PS is

characterized by a very large internal surface. Porous silicon formed

under different anodization conditions exhibits a variety of rich and

complex structure with many features [40].

۱۰


Porous silicon (PS) 1.10

The technology of porous silicon seems to have advantages since

the specific dimensions of PS stem can be reduced down to nanometre

size. It is reasonable to expect significant increase of detector’s

sensitivity if PS technology were introduced in its production. Additional

advantages are expected due to the quantum confinement effect, which is

obtained conventionally by anodization of silicon substrates. Crystallites

of silicon formed by this means can present diameters varying from units

of nanometers to tens of micrometers, depending on formation parameters

(current density, electrolyte concentration, etching time, and substrate

type). This characteristic, that is, the possibility of porosity control,

makes PS suitable for several applications on gas sensing.

Porous silicon technologies have many applications in

semiconductor technology, optoelectronics, chemical, biological sensors

and other fields of science. Electrochemical etching of a silicon wafer

surface, under different conditions and additional processing, changes the

optical and electrical properties of porous silicon layers widely.

The physical properties of porous silicon are fundamentally determined

by the porosity of pores [41,42,13].

1.11 Preparation Techniques

1.11.1 The Etching Process

Various etching techniques can be divided into wet and dry

categories according to the chemical reaction on the gas-solid and liquid-

solid interface. In the wet etching, chemical acid solutions are used to

dissolve silicon substrate by chemical reactions [43]. Wet etching of

silicon can be achieved in different ways [44,45]:

۱۱


• Laser Induced Etching process (LIE)

• Photochemical Etching process (PCE)

• Photo electro Chemical Etching process (PECE)

• Stain Etching process

• Electrochemical Etching process

in our work Photochemical Etching process used

1.11.2 Photochemical Etching Mechanism

A silicon wafer is known to be inert in Hydro Furan Acid acid but a

chemical reaction can be initiated when holes reach the surface.

Therefore, in an n-type silicon valence-band holes are required at the

sample surface for porous silicon formation [46]. Photochemical technique

has been used to produce PS, which does not involve an externally

applied bias. In this technique, the light (laser) is used to supply the

required holes in the irradiation area of Si wafer to initiate the process[47]

.Generally, when a semiconductor is immersed in an aqueous solution

that contains electron acceptor species, charge transfer occurs at the

semiconductor-electrolyte interface. This charge transfer creates a space-

charge layer in the semiconductor resulting in a band bending upward in

an n-type And downward p-type material [48]. An n-type Si wafer is

immersed in aqueous HF acid and illuminated with laser light, a large

number of electron-hole pairs are generated in (C-Si) in the irradiated

area. a percentage of both charges will diffuse rather than immediately

recombine due to the indirect band gap in silicon. Furthermore, because

of the internal field caused by band bending, holes are driven into the

surface to initiate the etching process. These holes help to substitute

fluoride by hydrogen on the passivity Si surface and a Si-F bond is

established Due to the polarizing influence included by the Si-F, the

electron density of the Si-Si bond is lowered, which is further attacked by

۱۲


HF finally, the detachment of a Si atom occurs in the form of SiFR4 Ror

SiFR6R as etch products.See fig (1-5).

The chemical reaction of this process can be expressed as follows.

↑++−→+++ 2421242 HSiFHnSihFHnSi ………..(1-3)

On the other hand, electronically current flows from the back side of

the wafer through the electrolyte completing the electrical circuit and this

current enhances the etching process in the wafer thickness direction.

The electrical field effects can lead to preferential transport of

holes to the bottom of pores rather than to pore walls. This leads to

preferential etching at the bottom of the pores and since there is no

applied potential, the only source of an electrical field inside the Si would

be from band bending while there is certainly a band offset between bulk

Si and a PS layer at the interface, this band offset, which results from

quantum confinement, is sufficient to lead to a focusing effect.

It is expected that the microstructures and properties of the produced PS

material would depend upon the processing parameters, such as the

photon energy, power density and irradiation time. It is of great interest

both to develop a control of the fabrication process and to monitor the

size of the nanostructure in the PS samples. Therefore, for more detailed

investigation and characterization of the constituent nanostructure,

Raman and PL spectroscopies are often employed. These can give us

significant information on the size distribution of the nanocrystallites

present in laser etched PS [49,50].

۱۳


Figure(1-5): Diagram of the reaction mechanism for PS formation [51].

1.12 Types of Optical Detectors Optical detectors are usually divided into two broad classes:

photon detectors and thermal detectors. In photon detectors, quanta of

light energy interact with electrons in the detector material and generate

free electrons. To produce free electrons, the quanta must have sufficient

energy to free an electron from its atomic binding forces. The wavelength

response of photon detectors shows a long-wavelength cutoff. If the

wavelength is longer than the cutoff wavelength, the photon energy is too

small to produce a free electron and the response of the photon detector

drops to zero.

Thermal detectors respond to the heat energy delivered by light. These

detectors use some temperature-dependent effect, like a change of

electrical resistivity. Because thermal detectors rely on only the total

amount of heat energy reaching the detector, their response is

independent of wavelength. The output of photon detectors and thermal

detectors as a function of wavelength is shown schematically in Fig ( 1-

6). This figure shows the typical spectral dependence of the output of

photon detectors, which increases with increasing wavelength at

wavelengths shorter than the cutoff wavelength. At that point, the

response drops rapidly to zero.

۱٤


The figure also shows how the output of thermal detectors is

independent of wavelength, and extends to longer wavelengths than the

response of photon detectors[52].

1.12.1 Thermal detectors

Thermal detectors are sensing the changing in temperature

produced by absorption of incident radiation. In thermal detectors, the

radiation is absorbed by the lattice of material, causing heating of the

lattice. The change in the temperature of the lattice by the absorption

causes a change in the electrical properties. These detectors are generally

operated at room temperature. Fig (1-6) shows the mechanism

responsible for the absorption of the radiation which is itself wavelength

independent [53].

Figure(1-6): Relative spectral response for a photo detector and a thermal

detector [55].

1.12.2 Photon detectors

Photon detectors respond in proportional to incident photon rates

rather than to photon energies (heat). Thus , the spectral response of an

۱٥


ideal photon detector is flat on an incident-photon-rate basis but linearly

rising with wavelength on an incident-power (per watt) basis .In photon

detectors the incident photons are absorbed within the material by

interaction with electrons. The observed electrical signal results from

changing the electronic energy distribution. The photon detectors

measure the rate of arrival of quanta and show a selective wavelength

dependence of the response per unit incident radiation power as shown in

Fig (1-6) [54].

Photon detectors have a small sizes minimum noise, low biasing

voltage, high sensitivity, high reliability, and fast response time.

Basically, if a photon of sufficient energy excites an electron from

a nonconducting state into a conducting state, the photoexcited electron

will generate current or voltage in the detector. The electronic excitation

requires that the incident photon energy must be equal to or greater than

the electronic excitation energy. In other words, the excitation condition

is: νhexc ≤Ε .........1-4

or

cexc λ

242.1≤Ε

...........1-5

where ERexcR is the electronic excitation energy in electron volts.

λRcR is the free space wave length in micrometers.

h=P

P4.136×10 P

-15Pev.s ,C=3×10 P

8Pm∕s

Most of photon detectors have a detectivity that is one or two

orders of magnitude greater than thermal detector, and the response time

۱٦


of photon detectors is very short due to direct interaction between the

incident photons and the electrons of the detector material this interaction

is called photo effect.

Photon detectors include photoconductive (PC), photovoltaic (PV)

Photoemissive detectors. While the study now is specializing in

photoconductive detectors; therefore, we will concentrate on it in next

part [56].

1.13 Photoconductive Detectors

Since the nineteenth century it has been known that certain

materials have the power of changing their resistance on exposure to

light. Such materials are known as photoconductors, which is one of the

first type of semiconductor photon detector. The photoconductive

detector consists of a single crystal of semiconductor material with two

ohmic contacts, and a voltage applied between them. The semiconductor

is conducting, and therefore some current flowing even without light

shining on material (dark current). See fig (1- 7).

Fig (1-7): photoconductive detector [57].

۱۷


The incident photon energy creates free carriers in the crystal and

changes the conductivity of the material:

)( he pne µµσ += ..........1-6

where : e is the electron charge , n is the electron concentration.

µReR is the electron mobility, p is the hole concentration.

µRhR is the hole mobility.

This type of detector can be used for automatic light control in

homes and office buildings to turn light on at dawn and off at dark . Also,

they are useful in optical signaling systems.

Photoconductivity involves several successive or simultaneous

mechanisms, namely absorption of the incident light, carrier

photogeneration, and carrier transport (including carrier trapping,

detrapping and recombination).The magnitude of the conductivity change

induced by irradiation depends upon the number of carriers produced per

absorbed photon (carrier generation quantum yield), and the mobility of

photogenerated carriers.The duration of this change depends upon many

factors, such as the lifetime of the carriers and the time for the carriers to

encounter a trap.Therefore, photoconductivity is also a valuable probe for

the electronic properties relating to the charge carrier mobility and

lifetime [58].

The electronic transitions in photoconductive devices include:

I. The intrinsic photoconductive type is produced when the incident

photons with energy greater than or equal to the energy band gap ( hυ

≥ERgR), then an electron-hole pairs will be generated, and can limit the

۱۸


maximum wavelength cutoff wavelength (λRcR) that detectors work is given

by eq(1-5) P

P.

II.The extrinsic photoconductive type : Since semiconductors have

states located ( energy levels ) either as donors or acceptors in the band

gap ; The energy required to ionize these must be smaller than the

intrinsic energy , so that the quantum energy with hυ > ERi R, where ERi

Ractivation energyR Rfor donors ( ERD R) or acceptor ( ERAR ) , is absorbed then

transition of electron from donor level to the conduction band for n-type

or, transition of holes from the valence band to acceptor levels for p-type

takes place but not both. In both cases the concentration of carrier

increases so that the conductivity of semiconductor will increase also .

This type is called photoconductive detectors as shown in figure (1-8)

.The cut off wave length ( λRcR ) is given by eq(1-5) P

P .

Figure( 1-8): Processes of photoconductive for semiconductor

(a) Intrinsic (b) Extrinsic P

[59]P.

Other types of photoconductivity are possible which are not

associated with a change in the free-carrier concentration. For example,

when long-wavelength electromagnetic radiation, which does not cause

interband migration and does not ionize impurity center, is absorbed by

free carriers, the energy of the carriers is increased. Such an increase

۱۹


leads to a change in carrier mobility and, consequently, to an increase in

electrical conductivity. Such secondary photoconductivity decreases at

high frequencies and is not frequency dependent at low frequencies. The

change in mobility upon exposure to radiation may be caused not only by

increasing in carrier energy but also by the effect of the radiation on

electron scattering in the crystal lattice [60].

1.14 The Figure of Merit

There are many parameters affecting the performance of the

detectors. These parameters are:

1.14.1 Responsivity ( RRλ R)

Responsivity is defined as the ratio between the output electrical

signals (voltage or current) to the incident radiation power or is defined as

the r.m.s signal voltage to the r.m.s value of the incident radiation power.

The responsivity for monochromatic light of wavelength incident

normally is given by[61] .

in

ph

PI

R =λ (Amp∕Watt) or inP

VR =λ (Volt∕ Watt) ……..1-7

where :

IRphR = photocurrent flowing between the electrodes.

V= signal voltage


The photocurrent gain G of a detector is defined as the number of

charge carriers flowing between the two contact electrodes of a detector

per second for each photon absorbed per second that is .

۲۰


rT

G τ= …………………… 1-8

where τ is the carrier lifetime , TRrR is the transit time , which is expressed

by :

B

r VT

⋅=µ

2 ……………………..1-9

where ℓ is the distance between electrodes , μ is the majority

carrier mobility , and VRBR is the bias voltage applied to the sample[60].

1.14.3 The Noise in Detectors (IRnR)

The noise is refered to the signal generated in the detector at the

absence of the radiation . The relation between dark current and noise

current is [57] :

IRn R= ( 2e IRdR Δf )P

1/2P …………….……..1-10

Where IRd R is dark current , Δf is bandwidth.

1.14.4 Noise Equivalent Power ( NEP)

NEP is defined as the root mean square ( r.m.s ) incident radiant

power falling on the detector that is required to produce an ( r.m.s ) signal

voltage or current equal to the ( r.m.s ) noise voltage or current at the

detector output . It is expressed as [62]:

NEP = IRn R/ RRλR …………………………….. 1-11

The detection capablility of the detector improves as the NEP

decreases .

۲۱


1.14.5 Detectivity ( D ) and Specific Detectivity ( D* ) :

The detectivity ( D ) is defined as the signal – to – noise ratio per

unit incident radiation power and it is defined as:

D = 1/NEP = RRλR / IRn R (WattP

-1P) …………1-12

Specific detectivity D* (normalized detectivity ) : it is the

detector signal – to – noise ratio when 1 Watt of optical power is incident

on the detector with optical area 1 cmP

2 Pand the noise is measured with a

band width of 1 Hz . It is used because it is normally dependent on the

size of the detector and the bandwidth of the measurement circuit, while

D depends on both . The peak value of D* at specific wavelength can be

written asP

P[63] ;

D* = D ( A Δ f )P

1/2 P …………….……….1-13

Or D* = RRλR ( A Δ f )P

1/2P / IRn R………….…..…… 1-14

The value depends on the wavelength of the signal radiation and

the frequency at which it modulated P

.

1.15 The mathematical model of the photoconductive

detector

The photocurrent generated in the detector circuit shown in figure

(2-5a) when the detector elements are illuminated by the UV radiation

can be written as[39,57];

GNei ...η= ……….1-15

where η is the quantum efficiency.

e is the electronic charge.

۲۲


N is the number of the absorbed photons per unit time.

G is the Photocurrent Gain.

TRrR is the transit time for majority carrier between the sample

electrodes.

Substituting eq. 1-8 and eq. 1-9 in eq. 1-15, one can get

2

BVNei ⋅⋅⋅⋅⋅=

τµη …….1-16

Since ch

WhWN

⋅⋅

=⋅

=λ

υ …….1-17

where W is the energy of the incident light , λ is the wavelength of

incident light, h is Planck’s constant, and c is the speed of light.

Substitute eq. 1-17 in eq. 1-16, the photocurrent can be written as:

2 ⋅⋅

⋅⋅⋅⋅⋅⋅=

chVWei Bτµλη

…. …..1-18

In the detector circuit shown in figure (1-9), the RRLR is the load resistance,

therefore, the variation in load voltage ∆VRLR is:-

LLd

dL R

RRR

iV ⋅+

=∆ ………1-19

where RRd R is the detector resistance.

۲۳


Figure (1-9): The operation circuit diagram of SnOR2R photoconductive detector

where; RRdR is the detector element, RRL Ris the load resistance and VRCR is the bias

voltage.

for RRdR >> RRLR

dL RiV ⋅≈∆∴ …….1-20

for dwRd ⋅⋅

=σ

……….1-21

where σ is the conductivity , w is the width of the detector and d is the

height of the detector.

Substitute eq. 1-18 and eq. 1-21 in eq. 1-20, the variation voltage across

the load resistance can be given as:

dwch

VWeV BL ⋅⋅

∗⋅⋅

⋅⋅⋅⋅⋅⋅=∆∴

σλτµη

2 …….1-22

Rd

VC

RL

0.1 μF Output

Detector

۲٤


Use µσ ⋅⋅= en and substitute in eq. 1-22, and rearrange the terms, the

above equation can be written as:

( )dwnchVWV B

L ⋅⋅⋅⋅⋅⋅⋅⋅

=∆∴

λτη …………1-23

The photoresponsivity RRλ Ris defined as the ratio between the output

electrical signal to the energy of the incident light. Then;

WVR L∆

=λ ………1-24

Substitute eq. 1-23 in eq. 1-24 RRλR can be written as:

( ) nchdwVR B

⋅⋅⋅⋅=

... λτηλ …… 1-25

This is the photoresponsivity of the photoconduction detector for thick

film (bulk) according to the circuit show in figure (1-7) .

nanofilms are used in this work, the above relation need to be

modified; a special modification was suggested by Suhail [64]for solving

the responsivity of the photoconductive detector in nanofilm and it can be

summarized as follow:

The quantum efficiency for a thin film detector is given by:

( )[ ]dαηη 2exp1 −−= ……….. 1-26

where:

ηRoR is the internal quantum efficiency , i.e the no. of electron-hole pairs

generated by absorbed photon, α is the absorption coefficient.

Substitute eq. 1-26 in eq. 1-25, the Responsivity is written by:

( )[ ]( )wdhcn

VdR B

...2exp1 λταη

λ−−

= …….. 1-27

۲٥


For a thin film detector, the absorption coefficient is low and the

condition 2αd << 1 is always fulfilled in the thin film detectors; the

efficiency can be written as:

( )dαηη 2= where ηRoR in this case equal to 1, then the relation 1-27 can

be written as:

( )wdhcndVR B

)2.(.. αλτλ = ……… 1-28

Relation 1-28 can be written as:

)(2...whcn

VR B

αλτλ = ………… 1-29

The bias voltage (applied voltage) VRBR is limited to the allowed

power that can be passed through the thin film detector. This is called the

bias power which is;

dRiu .2= …………… 1-30

where i is the circuit current, which is given by:

( )Ld

B

RRVi+

= …………. 1-31

Substitute eq. 1-31 in eq. 1-30, the bias power u is written as:

( ) d

Ld

B RRR

Vu .2

2

+= ……….. 1-32

For RRdR >> RRLR the bias power became:

d

B

RVu

2

= ……………… 1-33

۲٦


The bias power density ( )wRVu

d

B

⋅=′

2

…….. 1-34

Thus, ( )wRuV dB ⋅′= .. …… 1-35

Substitute eq. 1-35in eq. 1-29, and rearrange the terms, the following

formula can be considered:

′

=

nwuR

hcR d ταλλ

..2 2/1

……. 1-36

When the first term is constant, the second term is square root, and the

third term is linear. These results show that the photoresponsivity (RRλR) is

depending too much on the third term

nτα. .

1.16 Literature Survey Yang Liu1et.al (2000)[60] had synthesized two SnOR2R

nanoparticles by hydrothermal method at 170ºC and 180ºC, respectively.

Transmission electron microscope observations reveal that the diameters

of both the nanoparticles were around 6 nm. At the same time, surface

photovoltage spectroscopy measurements, showed that the nanoparticle

synthesized at 180ºC, had more surface electronic states at 0.3 eV below

the conduction band than the one synthesized at 170ºC. This means that

the temperature chosen in hydrothermal synthesis had significant

influence on the surface electronic characteristics of resultant SnOR2R

nanoparticles but the effect on their sizes was not obvious.

Feng Gu a et.al (2003)[65] had prepared SnOR2 Rnanoparticles by a

simple sol–gel method. XRD measurement indicates that the diameter of

the prepared particle was about 2.6 nm. FTIR and the UV–Vis absorptive

spectra of the samples had also been investigated. And the PL exhibits

۲۷


two bands at 400 and 430 nm, respectively. The luminescence was related

to the recombination of electrons in singly occupied oxygen vacancies

with photo excited holes in the valence bond.

SANJAY R DHAGE et.al (2004)[66] had reported that simple gel

to crystal conversion had been followed for the preparation of

nanocrystalline SnOR2R at 80–100°C under refluxing conditions. Freshly

prepared stannic hydroxide gel was allowed to crystallize under refluxing

and stirring conditions for 4–6 h. Formation of nano crystallites of SnOR2R

was confirmed by x-ray diffraction (XRD) studied. Transmission electron

microscopic (TEM) investigations revealed that the average particale size

was 30 nm for these powders.

J.J. Valenzuela-Ja et.at (2004)[67] had deposited metal films of Sn, In

and In–Sn on glass substrates at room temperature by means of the DC

sputtering technique.. A film of the corresponding metal oxides was

obtained after thermal annealing the metal for 1 h in air at temperature

from 350 to 500P

oP C. The oxide film was studied besides that, transmission

and reflection spectroscopy, by measurements of their sheet resistance

between coplanar electrodes. The results showed that materials with the

properties of transparent conductive oxides (TCO) films could be

obtained by this process.

Luhua Jiang et.al (2005)[68] had synthesized tin oxide

nanoparticles by heating ethylene glycol solutions containing SnClR2R at

atmospheric pressure. TEM micrographs showed that the obtained

material were spherical nanoparticles, the size and size distribution

depends on the initial experimental conditions of pH value, reaction time,

water concentration, and tin precursor concentration. The XRD pattern

۲۸


result showed that the obtained powder was SnOR2R with tetragonal

crystalline structure. On the basis of UV/VIS and FTIR characterization,

the formation mechanism of SnOR2R nanoparticles was deduced.

Chunjoong Kim et.al( 2005) [69] SnOR2R nanoparticles with

different sizes of 3, 4, and 8 nm had been synthesized using a

hydrothermal method at 110, 150, and 200 C, respectively. The results

showed that the 3 nm-sized SnOR2R nanoparticles had a superior capacity

and cycling stability as compared to the 4 and 8 nm-sized ones. The 3

nm-sized nanoparticles exhibited an initial capacity of 740 mAh/g with

negligible capacity fading. Transmission electron microscope(TEM) and

X-ray diffraction (XRD) confirmed that the 3 nm-sized SnOR2

Rnanoparticles after electrochemical tests did not aggregate into larger Sn

clusters, in contrast to those observed with the 4 and 8 nm-sized ones.

K. ANANDAN et.al (2008)[32] had synthesized tetragonal phase

SnOR2R nanocrystals via facile solvothermal process by using SnClR4R.5HR2RO

and HCl at different temperature. The phase, size and purity of the

resultant products were characterized by means of powder X-ray

diffraction (XRD).

M. M. Bagheri-Mohagheghia et.al (2008)[70] Nano-crystalline

SnOR2 Rparticles had been synthesized by sol–gel process using a simple

starting hydro-alcoholic solution consisting of SnClR4R, 5HR2RO and citric

acid as complexing and ethylene glycol as polymerization agents. The

XRD patterns showed SnOR2R-cassiterite phase in the nano-powders, and

size of crystals increases by increasing the annealing temperatures. The

optical direct band gap values of SnOR2R nano-particles were calculated to

be about 4.05–4.11 eV in the temperature range 300–700º C by optical

absorption measurements. These values exhibited nearly a 0.5 eV blue

shift from that of bulk SnOR2R (3.6 eV), which was related to size decrease

۲۹


of the particles and reaching to the quantum confinement limit of nano-

particles.

S. MAJUMDER(2009)[71] had fabricated SnOR2R thin films by a

wet chemical process, using SnClR2R·2HR2RO as a tin containing precursor.

The films obtained were subjected to optical, X-ray diffraction (XRD),

microstructural, FTIR and Raman studies.

Rohana Adnan et.al (2010)[ 72] had prepared SnOR2R nanoparticles

using a simple sol-gel technique with varying reaction parameters such

as concentration of ammonia, ammonia feed rate and reaction

temperature. The Size obtained was in the range of 4 to 5.6 nm and the

surface area was found to be between 76 to 114 mP

2P.

Lucky M Sikhwivhilu et.al (2010)[73] had synthesized tin oxide

(SnOR2R) nanoparticles by using wet chemical process (i.e. chemical

precipitation and sol-gel processes). The results showed that variation of

citric acid concentration directly influences the particle size and the BET

specific surface area with size range of 19 to 100 nm.

L. C. Nehru et.al(2012) [74] Nanocrystalline tin oxide (SnOR2R)

powders were been synthesized by a low temperature chemical

precipitation method. Crystallographic parameters such as crystallite size,

lattice parameters and dislocation density in SnOR2R nanocrystalline

powders were calculated by Rietveld analysis. The average crystallite size

of 9 - 43 nm was obtained for SnOR2R powders through controlled heat

treatment process. The washed powders morphology was almost

spherical in shape and average agglomerate crystal size was between 0.2

– 0.4 μm.

Ganesh E Patiletet.al (2012) [75] Preparation and characterization

of SnOR2R nanoparticles by hydrothermal route had been demonstrated

SnOR2 Rnanoparticles using a simple hydrothermal route in the presence of

۳۰


the surfactant hydrazine at 100 °C for 12 h. The XRD pattern of the as-

prepared sample was indexed to the tetragonal structure of SnOR2R, and the

calculated particle size was 22.4 nm, which was further confirmed by

TEM. Spectrum showed the band gap of the synthesized SnOR2R was 3.6

eV.

1.17 Aim of the Present work

In this work the SnOR2R nanopowder was deposited on porous silicon

by dip coating technique to form UV photoconductive detector in order to

improve the response time of the detector. The improvement based in two

mechanisms the first is improve the structure of coating film on the

silicon layer through developing the porous layer on n-type silicon

substrate and the second is the functionalization of the detector surface by

coating the sensitive area by poly amide nylon polymer.

Chapter Two

Experimental Work

۳۱

Chapter Two The Experimental Work

2.1 Introduction In this chapter the preparation of SnOR2R nanopowder by Sol gel

method was presented. And the fabrication of SnOR2R-UV photoconductive

detector is included. The enhancement of the fabricated detector was

carried out by coating the detector with polyamide nylon polymer.

The X-Ray diffraction (XRD) pattern was used to study the

structure of the samples. The photoluminescence spectrum, the UV –

Visible absorption spectra of the SnOR2R nanopowder and Hall

measurements were registered for the prepared samples.

The morphology of the nanospikes surface produced by

photochemical etching on Si wafer was studied using AFM. The

nanospikes silicon layers were used as a substrate for the Sno2

photoconductive detector elements.

The detector characterization measurements at room temperature

were presented for the fabricated detectors under the illumination with

UV-source. The SnOR2R photocondutive detector output signal was

displayed by a digital oscilloscope .

2.2 Silicon wafer properties.

n-type Si with resistivity (ρ= 0.05 Ω.cm) and (111) crystalline

orientation were employed as substrates with dimensions of (2 x 2cmP

2P)

to prepare PS using photochemical etching process . The sample

thickness of about 500 μm was used .

۳۲


2.3 Sample Preparation

The manufacturing of PS relies on the wet etching of wafers .

silicon substrates of (2x2cmP

2P) dimensions are cleaned to remove any

contamination on the surface, and the following cleaning procedures were

carried out :

1 -The silicon wafers were washed in diluted HF ( 1:10 ) concentration

for 15 min.

2- The wafer then immersed in distilled water for several times, and later

they were rinsed in methanol for 10 minutes and also in distilled water.

3- Finally, the samples were dried in oven, at 50P

ºPC.

2.3.1 Preparation of porous silicon layer by photochemical

etching

The photochemical etching is electrodeless process since there is

no applied bias voltage during the etching, This process is carried out by

using ordinary light source.

The setup shown in fig (2-1) has been used for the photochemical

etching process. The setup consists of a Quartz Tungsten Halogen lamps

(250W) integrated with dichroic ellipsoidal mirror supplied from Philips

Company , focusing lens and the diluted etching acid in Teflon container .

۳۳


Figure (2-1): The set up of the photochemical etching process,(photograph of the

system).

The n-type Si wafer of ( 0.05 Ω.cm ) resistivity was used as a

starting substrate in the photochemical etching. The samples of ( 2 x 2

cmP

2P ) dimensions were cut from the wafer and rinsed with acetone and

methanol to remove dirt. In order to remove the native oxide layer on the

samples, they were etched in diluted (10 %) HF acid. After cleaning the

samples they were immersed in HF acid of 50 % concentration and

ethanol (1:1)) in a Teflon beaker. The samples were mounted in the

beaker on two Teflon tablets in such a way that the current required for

the etching process could complete the circuit between the irradiated

surface and the bottom surface of the Si sample.

Conecting wire

Power Supply

lens

Teflon container

Light Source

۳٤


The light source was vertically mounted by a holder above the

sample, aligned and focused by Quartz lens of (3.87cm) focal length to

form a circular spot with a suitable power density. The lens was mounted

on a driven holder for precise focusing adjustment. The distance from the

lamp to the lens was about 30 cm and from the lens to the sample 14 cm.

The PS was formed on the illuminated side of the sample. The

photoetching irradiation times was chose to be about 10 minutes

At the end of the photochemical etching process, the sample were rinsed

with ethanol and stored in a glass containers filled with methanol to avoid

the formation of oxide layer above the nanospikes film. The nanospikes

silicon layers were used as a substrate for the SnOR2R photoconductive

detector elements.

2.4 Preparation of SnOR2R nanopowder by Sol gel method

SnOR2R nanopowders were prepared by means of dissolving 2 g

(0.1 M) of tin tetrachloride (SnClR5R.5HR2R O) in 100 ml distilled water.

After complete dissolution, ammonia solution was added to the above

solution by drop wise under stirring until pH was 1. The dropping rate

must be well controlled for chemical homogencity. White gel precipitate

is formed and its allowed to settle for 12 h. then the result gel were

washed and filtered with distilled water and then dried at 80P

oPC for 24

hours in order to remove water molecules. Finally Tin Oxide

nanopowder is formed at 500P

oPC.

2.5 Fabrication of SnOR2R/ps photoconductive detector

2.5.1 Preparing the solution

The nanopowder obtained by sol gel technique was added to the

distilled water under stirring, the obtained solution were used for films

۳٥


deposition on porous silicon and glass substrate by dip-coating technique

with a pulling rate of 5cm/3min. After each dipping process the

deposited film is heated at 150P

o PC for 5min. When the number of 5 layer

is reached, the Films are annealed at 500P

oP C for 2 hour in air.

2.5.2 The mask

In order to fabricate the photoconductive detector a special mask

needs to be fixed carefully on the surface of SnOR2R layer. Interdigitated

Aluminum ohmic metal contacts are deposited on the SnOR2R films by

using vacuum evaporation technique. Aluminum electrodes are made by

evaporation of Aluminum (Al) under vacuum with the help of the mask

Fig (2-2a) shows the schematic diagram of interdigital electrodes

of the SnOR2R UV detector, in which the gray and white part are SnOR2R

and electrodes respectively. The thickness of Al electrodes is 500 nm and

the distance between two electrodes are 0.4 mm. The photographic plate

of the mask is shown in fig (2-3b).

(a) (b)

Figure (2-2): (a) Schematic diagram of interdigital electrodes,(b) Photographic plate of

photoconductive mask.

SnO2 film

Finger Spacing 0.4mm

Electrode

25mm

10mm

۳٦


2.6 Fabrication of SnOR2R/si ps photoconductive( UV) detector

coated with a polymer

In order to improve the response time of the SnO2/ps

photoconductive UV detector a special, kind of polymer, that have high

UV absorption abilities, are used in the experiment.

The effect of the polymer type polyamide nylon on the enhancement of

the UV response of the SnOR2R on porous silicon UV detector is tested.

2.6.1 Chemical material:

Polyamide nylon from hexamethylene diamine and adipic acid of

a chemical structure shown below P

[59]P :

is used in the present work.

2.6.2 Coating of the SnOR2R films/PS by the polymer

The above polymer is used in coating the fabricated

SnOR2R/PS photoconductive detector by coating the sensitive of area the

detector by the above mentioned polymers as follow ;

0.16 gm of polyamide nylon polymer is dissolved in 5ml Tetra

Hydro Furan (THF) . This solution is stirred with the help of magnetic

stirrer , then the sample coated with polyamide polymer solution by the

help the spin coating technique.

۳۷


2.7 Atomic Force Microscope (AFM)

Atomic Force Microscopy studies was recorded by using Scanning

probe Microscope (type AA3000 , supplied by Angstrom Advanced Inc

.USA). as shown in fig (2-3).The unit is used to determine the nanosipkes

dimensions range of the prepared SnOR2R on PS and porous silicon

nanospikes layer and their statistical distribution.

Figure( 2-3): Scanning probe Microscope( Type AA3000) AFM.

۳۸


2.8 Structure Measurements :

2.8.1 X-Ray Diffraction studies

The X-ray diffraction (XRD) pattern of the SnOR2R nanofilm

deposited on n-type silicon substrate was recorded by SHIMADZU

XRD-6000 X-ray diffractometer (CuKRα Rradiation λ=0.154nm) in 2θ range

from 30 P

°P to 60P

°P.as shown in the figure ( 2- 4 ) .

Figure (2- 4) : XRD-6000 X-ray diffractometer (CuKRα Rradiation λ=0.154 nm ).

The interplaner distanced (h, k, l) for different planes are measured by

Bragg's law[57]:

2dsinӨ = n λ ………………. 2-1

۳۹


The d-values are compared with the ASTM (American Society for

Testing Materials) cared data file for SnOR2R.

2.8.2 Optical Properties

2.8.2.1 UV – VIS absorption spectrum

The absorption spectrum of the samples is measured using

OPTIMA SP-3000 UV–VIS spectrophotometer covering a range from

(200 – 1200) nm by using glass substrate as a reference. The absorbance

is measured for SnOR2R nanofilms on glass substrate. The measurement of

absorbance as a function of wavelength is used to calculate the absorption

coefficient (α) and the optical energy gap ( ERgRP

optP ).

The optical energy gap can be estimated by calculating the absorption

coefficient (α) which depends on the film thickness (length of the

absorption media) and absorbance, as given in the following equation:

=

dA303.2α …………….(2-2 )

where A is the absorbance, and d is the thickness. Using the relation

between (αhυ )P

2P as a function of photon energy the energy gap can be

determined by applying the Tauc equation [76] for direct transition as in:

αhυ = B ( hυ – ERgRP

optP ) P

rP ……… (2-3)

where B is a constant , hυ is the photon energy (eV) , α is the absorption

coefficient ( cmP

-1P ) , ERgRP

optP is the optical energy gap (eV) , r is a parameter

that has different values ( 1/2 , 3 , 3/2 , 2 ) [77].

The actual values of the optical energy gap are extracted from the

direct transition peak found in the photoluminescence spectrum.

٤۰


2.8.2.2 Photoluminescence Spectrum (PL)

The photoluminescence spectrum of SnOR2R nanofilm on porous

silicon is plotted using SL 174 SPECTROFLUOROMETER covering a

range from (200 – 900) nm.

2.9 Electrical Properties of the detector

2.9.1 Hall Effect Measurement

The Hall Effect measurement is determined by using HMS3000

Hall measurement setting. In order to determine the semiconductor film

type, the density of charge carriers, and the Hall coefficient of the film

need to be determined by Hall Effect study. The SnOR2R film on porous

silicon and glass substrate is prepared for such measurement.

After the formation of the SnOR2R nanofilm on substrates, the

attachment of metal mesh collector grid is formed. The grid of pure

Aluminum is fabricated by using vacuum evaporation technique with the

help of special mask, as it is shown in fig (2-5).

Figure ( 2-5):Schematic Mask for the Hall effect measurement.

٤۱


An electrode must be on the surface of the SnOR2R nanofilm.

Aluminum which is an ohmic contact used as grid, the ohmic contact

made by evaporation of Aluminum under vacuum with the help of the

mask and this mask is fixed carefully on the surface of SnOR2R layer.

2.9.2 Detector Characteristic Measurement

In order to determine the detector parameters, mainly the

Responsivity , the response time and the specific detectivity ( DP

*P ) of the

fabricated SnO2 nanofilm on PS photoconductive UV detectors, a

suitable setup is prepared for this purpose. The system consists of:

HUIER DC power supply (ps-1502DD), variable resistance used to limit

the detector bias current , PC-interfaced digital Multimater, and Laptop

PC as shown in figure (2- 6). The UV – LED is used as a UV source for

illumination of the SnO2 photoconductive UV detector. The power of the

LED is 2.5mW and wavelength of about 385 nm and it is working with a

bais voltage of 5V, 11 mA.

The variation of photoresponsivity of SnOR2R sample and response

time of the prepared detector was tested by illumination the fabricated

detector with chopped UV-LED. The measuring circuit is shown in Fig

(2.7). The SnOR2R photocondutive detector output signal was displayed by

digital oscilloscope of 200 MHz model TDS 202413 from Tektronix.

٤۲


Figure ( 2-6): Schematic diagram of the experimental setup.

D.C. Power

Supply

Variable

Resistanc

UV-source SnO2-detector

PC – interfaced Digital Multimater

Laptop PC

USB interface

Cable

Optical Bench

A A D.C. Power

Supply

Variable

Digital Multimater

Rd

Chapter Three

Results and Discussion

٤۳

Chapter Three Results and Discussion

3.1 Introduction

This chapter presents the results and the analysis of the

experimental measurements of the SnOR2R films and the SnOR2R-UV

photoconductive detectors.

The results include the X-ray diffraction test, optical properties, and

photoconductive properties of SnOR2R films which are prepared by Sol-gel

method that has been tested.

Finally, the enhancement of the fabricating detectors by using

polymer is studied also chapter.

3.2 Structure Properties

3.2.1 X-ray diffraction results of SnOR2R film

The X-ray diffraction (XRD) pattern of SnOR2R nanoparticles powder

is shown in Fig.(3-1) The peaks at 2θ values of 26.6°, 33.8°, 37.9°, 51.8°,

and 54.7° can be associated with (110), (101), (200), (211) and

(220)planes respectively. The SnOR2R product shows tetragonal structure,

which are in good agreement with other literatures. The average particle

size (D) was determined using the Scherer P

,Ps eq equation [ 78]:

1.3...........cosθβλKD =

1Twhere D is the crystallite size, K is the shape factor, being

equal to 0.9 , λ is the X-ray wavelength, β is the full width at half

maximum of the diffraction peak, and is the Bragg diffraction angle

in degree. The average particles size was found to be in the range of

8-10nm [74] .

٤٤


1T3.2.2 1TAtomic Force Microscopy

The AFM studies are focused on the characterization, at nanometric

scale, of the porous silicon layers, specially used for the study of layer

inhomogeneities , surface roughness of the substrate , and morphology of

porous silicon . For many studies, SPM is applied together with another

optical characterization or morphological technique.

1TThe fig(3-2a) shows that the nanospike distribution for 10 minute

etching time is nearly uniform with few nanometer heigh and

average porous size 79.80nm 1T.

1T The formation of the nanospikes layer enhance the resistivity of

the silicon porous layer to the order of 1T10P

5 PΩ1T .cm [44,79]. This can be

110)( 101)(

211)(

200)(

Inte

nsity

(a.u

)

220)(

2Ɵ (Degree)

Figure(3-1) : XRD pattern of the SnO2 nanoparticles.

٤٥


attributed to several reasons ; the capturing of the charge carriers by

the traps at the nanospikes, the diffusion of the impurity atoms to the

electrolyte, or to the wall of the pores and may be due to the

passivation of the impurity atoms with hydrogen [80,81].

1TFigure (3-2a): 2D×3D Scanning probe microscope image of porous silicon

layer of 10 min etching time.

٤٦


The SPM image of the surface morphology of the SnOR2R film had agood a uniform surface homegensity and gives a good indicator for formation of the SnOR2R nanoparticles. The average particle size determined from SPM, is about 73.65 nm, as shown in Fig. (3-2b).The surface morphology of SnOR2R film as observed from SPM image proves that the grains are uniformly distributed for 3D views.

The results are obtained from the SPM of the SnOR2R nanoparticles show

that the histogram of the percentage of SnOR2R as a function of the grain

size .

(1) 1T (2)

1TFig.(3-2b):SPM image of SnOR2R nanoparticles on PS with etching time 10

min.

Granularity Cumulation distribution Chart.

SPM of SnO2 nanoparticles

٤۷


0

0.5

1

1.5

2

2.5

3

250 300 350 400

3.3 Optical Properties

The optical properties of the prepared SnOR2 Rfilms have been

investigated. The properties include the UV-VIS absorption and the

Photoluminescence Spectrum(PL) spectra of the products.

3.3.1 UV-VIS absorption Spectrum

1TThe absorption spectrum of SnOR2R deposited on glass substrate is

shown in Fig(3-3). The figure shows high absorbance in the UV region,

whereas it's transparent in the visible region.

λ (nm)

Abs

orba

nce

Figure(3-3): The absorption spectrum of SnO2.

٤۸


3.3.2 The energy band gap calculation The optical band gap energy (ERgR) of the semiconductor is calculated from

Tauc relation (2-3) [ 24]. A plot of (αhν)P

2 Pversus hυ shows intermediate

linear region, the extrapolation of the linear part can be used to calculate

the ERgR from intersect with hν axis as shown in Fig(3-4) .The resultant

values of ERgR for SnOR2R is found to be about 3.7eV and 4.3 eV[80] , 1TThe

above two values may be related to the formation of nanostructures of

SnOR2 Rand the bulk SnOR2R1T, these values show a good agreement with the

values published by other workers. [81,82].

Figure(3- 4) : Plot of (αhυ)2 versus photon energy (hυ) for SnO 2.

٤۹


3.3.3 The optical Photoluminescence spectrum The photoluminescence emission spectra of SnOR2 Rnanoparticles at

280nm excitation is shown in Fig (3-5).when 1TSnOR2R1T nanoparticles exhibit

emission at 437nm. The emission maximum of 437 nm is lower than the

band gap of SnOR2R bulk, this peak can be attributed to the contribution of

oxygen vacancies and defect in the 1TSnOR2R nanoparticles [83,81] 1T.

λ (nm)

Figure(3-5): Photoluminescence emission spectra of SnOR2.

1T3.4 Hall Measurements

1T The Hall measurements show 1Tthat the SnOR2R nanofilm deposited

on glass substrate is n-type semiconductor. The Hall parameters for n-

type nanofilms which included (resistivity, conductivity , and Hall

coefficient ) at etching time (10min) were illustrated in table (3-1).

Inte

nsity

(a.u

)

٥۰


Table (3-1): Hall effect parameters for SnOR2R film deposited on porous silicon.

3.033E+0 1TResistivity ( ρ )1T (Ω.cm)

3.297E-1 1TConductivity1T ( 1/ Ω cm)

-4.903E+1

1T Average Hall (mP

2P/c )

-1.273E+17 1TBUIK1T Concentration (cmP

-3 P) P

1.616E+1 1T/vs ) Mobility(μ )( cmP

2

3.5 The Photodetector Measurements

The photodetector measurements of the fabricated SnOR2R on PS -

UV photoconductive detector have been investigated. The measurements

include the I-V characteristics , the specific detectivity , the photocurrent

gain , and the response time.

3.5.1 I-V Characteristics

The current-voltage (I-V) characteristics of the fabricated device of

10 min etching time is illustrated in figure (3-6). The dark(IRdR) and

photo(Ip ) currents are increased with increasing the bias voltage. The

linear behavior may be related to the ohmic nature of the detector

sample. All samples used in the experiments of the photoresponsivity

measurements of the prepared detectors are carried out under identical

experimental conditions . The conditions are ; the distance between the

light source and the measured sample, the wavelength and the power of

the UV source , the area of the UV light incident on the sample, the

distance between the electrodes mask, and the applied bias voltage.

From the figure (3- 6 ) , it can be observed that the dark current is

very low under the illumination by visible light and the photocurrent is

٥۱


highly increased under the illumination by UV source with wavelength

385nm and 2.5 mW incident power.

Figure ( 3-6 ):The variation of the photocurrent of the fabricated SnOR2R UV detector on

porous silicon layer as a function of the bias voltage at etching time 10min.

The increase of the photocurrent of the polymer coated SnOR2R / PS

photoconductive UV detector samples are much higher than that of the

uncoated detectors samples as shown in fig (3-7).

0

20

40

60

80

100

120

140

160

0 1 2 3 4 5 6

I-dark+PS+SnO2

I-UV light+PS+SnO2

٥۲


Figure ( 3-7 ):The variation of the photocurrent of the fabricated SnOR2R UV detector on

porous silicon layer as a function of the bias voltage with coated polymer at etching time

10min.

1TFigure1T( 3-7 ) shows the variation of the photocurrent of the fabricated SnOR2R UV detector on porous silicon layer at etching time of 10min as a function of the bias voltage 1T.The dark current is found to be about 95µA at 5 V bias whereas the photocurrent is 251µA at the same bias votlage. This result reflects a good UV radiation sensitivity with photoconductive gain 1T(G) 1Tof more than 2.64.1T The photoconductve gain (G), which is calculated from the ratio between the photocurrent to the dark current at the same bias voltage, is given by the equation ( 1-8). Also ,the carrier life time (τ) was calculated after calculate TRr R(transit time), eq(1-9), using the values of G = 2.64, µ= 1.616×10 cmP

2P/ V.s as found from Hall

measurements, L = 0.04 cm and V = 5 V the carries life time (τ) was found to be about 50µs This result gives a good value for response time of the SnOR2R detector.

.

٥۳


3.5.2 The Specific Detectivity ( D*)

The specific detectivity D P

*P which is sometime called the

normalized detectivity , is the reciprocal of the Noise Equivalent Power

(NEP) normalized to the detector area of 1 cmP

2P and a noise of the

electrical band width ΔfR Ris 1 HZ.

1T This detector parameter is calculated for the fabricated

photodetector elements referring to equations; (1-12and1-16) , and

using the values of IRdR = 95 µA at the bias voltage of 5 V , 1TΔ1Tf = 1 Hz ,

photo responsivity RRλR = 0.1 A/W at λ=385nm, A = 1cmP

2P and IRnR = 5.561T

1T10P

-12PA , the specific detectivity of the fabricated SnOR2R UV detector

deposited on porous silicon layer is found to be 1.81T 1T10P

10 P cm.P

PHzP

1/2P.

WP

-1P.


The photocurrent gain is calculated using equation (1-10) for the

polymer coated and uncoated SnOR2R UV photoconductive sample. The

average value of the gain registered for the polymer coated UV SnOR2R

photoconductive detectors under the same measurement conditions is

found to be about 2.64 , whereas the gain without polymer ≈ 2.2

The above value reflects the effect of the nylon polymer coating on

the improvement of the gain of the fabricated detector.

Since the photoelectric current gain (G) is a function of electrodes

geometry. Thus the photoelectric gain can highly be improved by

reducing the electrodes spacing P

P[84].

×

×

٥٤


3.5.4 The Response Time

1TThe response time of the fabricated SnOR2R UV detector on PS layer

is tested by UV source1T with wavelength 385nm and 2.5 mW incident

power 1T. The trace of the output pulse on the digital oscilloscope of 200

MHz band width is illustrated in fig (3-8).

Figure(3- 8 ): The photoresponse time of fabricated SnOR2R UV detector1T.The time base on x-

axis is 500 μs/div.

1T It can be noticed from the output detector signal traced by the

oscilloscope that the rise time (10% -90%) is in the order of 1.5ms and

the fall time (1-1/e) is 1.5ms.

٥٥


3.6 Conclusion

1-The SnOR2R UV photoconductive detector samples prepared by Sol

gel method are fabricated, which indicate that the Sol gel method can be

considered as a good method to prepare SnOR2R nanopowder for the UV

detectors.

2- The PL spectrum of SnOR2R shows that excitation at 280nm, 1TSnOR2R1T

nanoparticles exhibit emission at 437nm. The emission maximum of 437

nm is lower than the band gap of the SnOR2R bulk, this peak can be

attributed to the contribution of oxygen vacancies and defect in the 1TSnOR2R

nanoparticles1T.

3- The functionalization of the SnOR2R samples surface by polymers

shows giant enhancement in the photoresponsivity.

4- The maximum responsivity was observed by the samples coated with the Polyamide nylon and it is about 0.1 A/watt and response time was about 50µs.

.

3.7 Suggestions of future work

According to our results, the following ideas are suggested

1-Synthesis SnOR2R samples is by using other techniques such as

pulse laser deposition technique on silicon substrate to improve

the quality of the film and to enhance the detector performance.

2- Doping prepared SnOR2 R with other material like fluorine and

Carbon nanotube to improve the response time and the

responsivity of the detector.

٥٦

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ISSN: 2319-8753

International Journal of Innovative Research in

Science,Engineering and Technology

(An ISO 3297: 2007 Certified Organization)

Vol. 2, Issue 12, December 2013

7068 www.ijirset.com yright to IJIRSETCop

Preparation and Characterization of SnO2

Nanoparticles Asama. N. Naje1 , Azhar S.Norry2, Abdulla. M. Suhail3

Lecture, Dept. of Physics , College of Science, University of Baghdad, Baghdad, Iraq1

M.Sc. student, Dept. of Physics , College of Science, University of Baghdad, Baghdad , Iraq2

Asst. Prof., Dept. of Physics , College of Science, University of Baghdad, Baghdad, Iraq, Dept of Optometry, Dijlah

University college, Baghdad, Iraq3

Abstract: Tin Oxide (SnO2) nanoparticles powder have been synthesized by chemical precipitation method. The samples were characterized by X-ray diffraction, UV-Visible absorption and scanning probe Microscope SPM. The X-ray analysis shows that the obtained powder is SnO2 with tetragonal rutile crystalline structure and the crystalline size in the range of 8-10nm. The SPM investigation reveals that the average particles size is 73nm. The optical band gap values of SnO2 nanoparticles were calculated to be about 4.3eV in the temperature 550 o C, comparing with that of the bulk SnO2 3.78eV, by optical absorption measurement.

Keywords: SnO2 nanoparticles, X-ray diffraction ,Morphology, Optical Properties.

I. INTRODUCTION

Nanometer-sized materials have recently attracted a considerable amount of attention due to their unique electrical, physical, chemical, and magnetic properties, these materials behave differently from bulk semiconductors. With decreasing particle size the band structure of the semiconductor changes; the band gap increases and the edges of the bands splits into discrete energy levels. These so-called quantum size effects occur [1-5]. These quantum size effects have stimulated great interest in both basic and applied research.

Tin oxide (SnO2) is one of the most intriguing materials to be investigated today, This is because tin dioxide is a well-known n-type semiconductor with a wide band gap of 3.6-3.8 eV [ 6-8], and for its potential application in transparent conductive electrode for solar cells a gas sensing material for gas sensors devices, transparent conducting electrodes, photochemical and photoconductive devices in liquid crystal display , gas discharge display, lithium-ion batteries, etc[9- 14 ]. Many processes have been developed to the synthesis of SnO2 nanostructures, e.g., spray pyrolysis, hydrothermal methods, chemical vapor deposition, thermal evaporation of oxide powders and sol–gel method [15-20 ]

In the present work the fabrication and characterization of crystalline SnO2 nanoparticles powder by chemical precipitation method was studied

II. EXPERIMENTAL WORK

SnO2 nanopowders were prepared by means of dissolving of 2 g (0.1 M) stannous chloride dehydrate (SnCl2.2H2O) in 100 ml distilled water. After complete dissolution, ammonia solution was added to the above solution by drop wise under stirring. The resulting gels were filtered and dried at 80ºC for 24 hours in order to remove water molecules. Finally, tin oxide nanopowders were formed at 550ºC for 2h.

The obtained samples were characterized by X-ray powder diffraction (XRD) using (XRD -6000), supplied by SHIMADZU. The surface morphology of the samples was observed by Scanning probe Microscope (SPM) by using CSPM AA3000, supply by Angstrom Company. Optical absorption spectra of the samples were taken with OPTIMA SP-3000 UV-VIS Spectrometer,. The room temperature photoluminescence (PL) spectra of SnO2 were recorded with SL 174 SPECTRFLUORMETER.

الخالصهفي هذه الدراسة تم تصنيع كاشف التوصيل الضوئي لألشعة فوق البنفسجية من المسحوق النانوي

اوكسيد القصدير المحضر بالطريقة الكيماوية ورسب المسحوق على الزجاج والسيلكون المسامي

ة بطريقة الطالء بالتغميس ، ثم اجريت الفحوصات التركيب المحضر بطريقة التنميش الضوئي

والسطحية والخصائص البصرية للعينات المحضرة.

تم فحص المسحوق النانوي اوكسيد القصدير بواسطة حيود االشعة السينية ووجد ان تركيبها

). 110,101متعدد البلورات ذات تركيب رباعي الزاويا مع اتجاهية بلورية عالية عند (

لمرسبه على لزجاج فجوات طاقه الدراسات البصرية ان الغشية اوكسيد القصدير ا وأظهرت

.437nmاثية عند طول موجي .ما طيف االنبعاث اظهر انبع 4.37e Vو 3.7eVمقدارها

بينت دراسة شكل السطح للمسحوق النانوي المرسب عل السيلكون ان معدل الحجم الحبيبي هو

73.65nm.

الجهد في حالة الظالم -من خالل التيار كتم دراسة الخواص الكشفية للكاشف المحضر وذل

بينت وكما 385nmوبطول موجي mW 2.5لدايود االشعة فوق البنفسجية ذو قدرة واألضاءة

.n-typeقياسات هول ان المسحوق النانوي المرسب على السيلكون السامي هو من نوع

بوليمر بنوع من ال اخيرا تم معاملة سطح اوكسيد القصدير المرسب على السيلكون المسامي

)polyamide nylon 0.1) لتحسين استجابية الكاشف الىA/W ثم تم قياس زمن االستجابة

وسجلت اشارة نبضة الخرج باالسيلسكوب الرقمي. 0.052msللكاشف المصنع وسجل قيمة

جمهورية العراق

وزارة التعليم العالي والبحث العلمي

كلية العلوم\جامعة بغداد

تصنيع ودراسة كاشف التوصيل الضوئي اوكسيد القصدير لألشعة فوق البنفسجية

رسالة مقدمة الى

جامعة بغداد–كلية العلوم

كجزء من متطلبات نيل درجة الماجستير

في الفيزياء

من قبل

شاكر نوري غافلازهار )۱۹۹٤اء ي(بكالوريوس علوم في الفيز

أشراف

د.عبد أل محسن سهيل أ.

م.د.أسامة ناطق ناجي ـه۱٤۳٥م ۲۰۱٤

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