Bandgap Engineering of the Amorphous Wide Band-Gap Semiconductor (SiC) 1-x (AlN) x Doped with Rare Earths and its Optical Emission Properties Roland Weingärtner.
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Bandgap Engineering of the Amorphous Wide Band-Gap
Semiconductor (SiC)1-x(AlN)x Doped with Rare Earths and its
Optical Emission Properties
Roland Weingärtner
Departamento de Ciencias – Sección Física – Grupo Ciencias de los Materiales
Pontificia Universidad Católica del Perú (PUCP)
San Miguel, 14th of April 2011
Outline
I Motivation and Introduction
Wide band-gap semiconductors
Band-gap engineering
Rare earth doping and optical emission
II First Results of a-(SiC)x(AlN)1-x
Thin film growth method and structural characterisation
Band-gap engineering of a-(SiC)x(AlN)1-x
III Cathodoluminescense measurements
Spectral emission of rare earth doped a-(SiC)x(AlN)1-x
Thermal activation of rare earth emission
IV Summary and Acknowledgements
1970 1975 1980 1985 1990 1995 2000 2005 20090
20
40
60
80
100
# of ar
ticl
es fro
m A
PS
journ
als
Year
GaN SiC AlN ZnSe
Combine the advantages of an insulator and a semiconductor
Principal idea:
Advantage of a semiconductor:
Advantage of an insulator:
Active electronic devices like diodes, transistors, etc
Due to the wide band-gap the samples are transparent
Why wide band-gap semiconductors ?
Historic development:
GaN based LED
Band-gap engineering
Variation of the band-gap by changing the composition
The band-gap has influence on:
Emission wavelength of an optical device efficiency of the light emission energy level of the dopants etc.
Choose an optimal composition for a specific application
AxB1-x
Small overview of semiconductors
Wid
e b
an
d-g
ap
Why rare earth doping in semiconductors ?
Optical emission properties of rare earths:
emission wavelength does not depend on the host material
Color is typical for a specific rare earth ion
Intensity of rare earth emission depends on the material:
band-gap quenching
temperature quenching
concentration quenching
Colors in rare earth doped GaN
M. Garter et al. Appl. Phys. Lett. 74 (1999) p.182
200 400 600 800 1000
Wavelength [nm]
Yb3+2F5/2 2F7/2
Sm3+4G5/2 6H7/2
4G5/2 6H9/2
CL I
nte
nsitie
s [
a.u
.]
Eu3+5D0 7F1,2
Tb3+5D4 7F5
Tm3+1G4 3H61D2 3H4
Dy3+
4F9/2 6H13/2
Excitation mechanism
1 and 2: excitation pathsa and b: recombination paths
RE3+ Ion
Cathodoluminescense of RE3+ in a-AlN:RE
Intrashell-transitions of f-shells
Temperature quenching of Er3+ doped semiconductors
From Favennec: Electronics Letters 25 (1989) 718
a) In0,16Ga0,38As0,84P0,16
b) Sic) InP d) GaAse) Al0,17Ga0,83Asf) ZnTeg) CdS
Incr
ease
of
ban
d-g
ap
Temperature quenching for Er3+ emission
From Zanatta: Appl. Phys. Lett. 82 1395 (2003)
Temperature quenching in AlN:RE
From Lozykowski and Jadwisienczak: Phys. Stat. Sol. B 244 (2007) 2109
Emission
1 expB
AI
Bk T
Phenomenological description:
Outline
I Motivation and Introduction
Wide band-gap semiconductors
Band-gap engineering
Rare earth doping and optical emission
II First Results of a-(SiC)x(AlN)1-x
Thin film growth method and structural characterisation
Band-gap engineering of a-(SiC)x(AlN)1-x
III Cathodoluminescense measurements
Spectral emission of rare earth doped a-(SiC)x(AlN)1-x
Thermal activation of rare earth emission
IV Summary and Acknowledgements
a-(SiC)x(AlN)1-x:RE
Why a-(SiC)x(AlN)1-x?
Rare earth doping:
Well defined emission color Covering of the whole color range
Wide bandgap semiconductors:
Increase of rare earth emission Lower temperature quenching Transparent Semiconductor devices
Amorphous films:
Inexpensive Simple production Higher incorporation of rare earths
Pseudobinary compound:
Band-gap engineering (3eV to 6eV) one composition parameter Sputtering from SiC and AlN target
Los principios de dc-sputtering
target
ánodo+
+
+
++
+
+
+ ion Ar
Átomo Arelectrón
Plasma frío: ion
electrón
10 3electrón
-4
300K
12000K
10 cm
grado de ionización: 10
T
T
n
10-2 mbarsustrato
-
+
Problemas:
Inestabilidad del plasma Sólo targets metálicos Baja eficiencia
1000 V
Los principios de magnetrón-sputtering
Aumento de densidad de los iones Más rapidez del crecimiento
El magnetrón
magnetrón armado
blindajeportatarget
N
NN
SS
S
Anillo de plasma
target
Schematics of the sputtering system
Turbo-molecular
pump
Mechanical pump
Pressure sensor
Mass spectrometer
control
Ar N2
Mass flow controler
Control of mass
spectrometer
Rf- generator
Rf-generator
shutterH2O
substrate
targets
flexiblemagnetrons
H2O
match
PC control
The rf magnetron sputter system at the PUCP
Vacuum system: residual gas analysis
Gas processing: flow control of N2, H2 and Ar:
0…100 sccm, 5N...6N
working pressure:
Sputter targets: trial magnetron sputtering, 2´´ 3 Rf generators, P<300W felxible target geometry !!
Substrates: Substrate area up to 128 cm2
variable target substrate distance water cooled substrate holder
78 10 mbarp
3 18 10 mbar 1 10 mbarp
A typical film of a-SiC on glas
0 1 2 3 4 5 6 7
Longitud [cm]
Esp
esor
[uu. aa
.]Target material: Silicon Carbide (SiC)
Substrate material: fused glas
Rf power: 100 W
Process gas: Argon, 5N
Gas flow: 80 sccm
Argon pressure: 810-3 mbar
a-SiC
3´
3´
1 2 3 4 5 6 7
Esp
esor [u
u. a
a.]
Longitud [cm]
distancia desde target: 6 cm 5 cm 4 cm 3 cm 2 cm
anillo delplasma
80403
80402
80401
80331
80327
Característica de emisión de un magnetrón I
3argón sputtering120 W, 9 10 mbar, flujo: 50 sccm, 5 hP p t
Característica de emisión de un magnetrón II
N
NN
SS
S
1cm
00.0200.0390.0590.0790.0980.120.140.160.180.200.220.240.260.270.290.310.330.350.370.390.410.430.450.47
emisión en uu. aa. Contorno de emisión
blindaje
plasma
target
imanes
3argón
sputtering
120 W
9 10 mbar
flujo: 50 sccm
5 h
P
p
t
A typical thin film of a-(SiC)x(AlN)1-x
EDX results
highly pure films (i.e. Na content < 8 ppm wt.) no signature of impurities in the film
0 20 40 60 80 100
0
10
20
30
40
50
60
70
80
positio
n (m
m)
content (at. %)
AlNAlN
SiC
Si Al Na Mg Ar Ca
host
substrate
Transmission electron microscopy (TEM):
Structure of a/nc-AlN and a-SiC anealed at 900°C
High resolution transmission electron microscopy (HRTEM):
There are nanocrystals embedded in an amorphous matrix
Substrate (Si)
a-SiC
diffraction
a/nc-AlN
a/nc-AlN
Optical absorption measurements
Determination of the band-gap i.e. a-(SiC)0.25(AlN)0.75 :
0.0
2.0x1010
4.0x1010
6.0x10101 2 3 4 5
1 2 3 4 50
400
800
1200
2-Plot fundamental absorbtion
Energy (eV)2
(cm
-2)
E= (3.7±0.1) eV
Urbach tail
E1
/2(e
V1/2cm
-1/2)
Energy (eV)
ETauc
= (2.4±0.1) eV
Tauc-Plot
Gap 2 11 1E x E x E b x x
0.00 0.25 0.50 0.75 1.000
1
2
3
4
5
6
AlNSiC
a- S
iCc-
SiC
6.2 eV
3C-SiC
6H-SiC4H-SiC
c- AlN
a-/nc-AlN, Ref [2]
a-AlN, Ref [3]
a-(SiC)1-x
(AlN)x, 2-Gap
a-(SiC)1-x
(AlN)x, Tauc-Gap
, c-(SiC)1-x
(AlN)x , Ref. [1]
E (eV
)
composition x
Band-gap engineering of a-(SiC)x(AlN)1-x
[1] Nurmagomedov et al.: Sov. Phys. Semicond. 23 100 (1989)[2] Gurumurugan et al.: Appl. Phys. Lett. 74 3008 (1999)[3] Zanatta et al.: J. Phys. D: Appl. Phys. 42 (2009) 025109
Bowing parameters: ba2=(1.98±0.94) eV , bTauc=(1.96±0.48) eV
Fitting to Vegard´s law:
Outline
I Motivation and Introduction
Wide band-gap semiconductors
Band-gap engineering
Rare earth doping and optical emission
II First Results of a-(SiC)x(AlN)1-x
Thin film growth method and structural characterisation
Band-gap engineering of a-(SiC)x(AlN)1-x
III Cathodoluminescense measurements
Spectral emission of rare earth doped a-(SiC)x(AlN)1-x
Thermal activation of rare earth emission
IV Summary and Acknoledgements
200 400 600 800 1000
Wavelength [nm]
Yb3+2F5/2 2F7/2
Sm3+4G5/2 6H7/2
4G5/2 6H9/2
CL I
nte
nsitie
s [
a.u
.]
Eu3+5D0 7F1,2
Tb3+5D4 7F5
Tm3+1G4 3H61D2 3H4
Dy3+
4F9/2 6H13/2
Emission of rare earth ions in a/nc-AlN and a-SiC
Cathodoluminescense of RE3+ in a-AlN:RE
400 500 600 700 800
a) a-SiC:Tb3+
CL
-In
ten
sity
[a
.u.]
5D4 7F
5
4F9/2
6H13/2
b) a-SiC:Dy3+
5D0 7F
1,2
c) a-SiC:Eu3+
Wavelength [nm]
Cathodoluminescense of RE3+ in a-SiC:RE
Thermal activation of a-/nc-AlN
0 200 400 600 800 1000 1200
C
L P
eak
Inte
nsi
ties
[a.u
.]
Temperature [°C]
Sm3+: 4G5/2
6H7/2
as grown
a/nc-AlN: RE3+
a)
Eu3+: 5D0 7F
1,2
Yb3+: 2F5/2
2F7/2
exponential growth with the anealing temperature there is a saturation of the RE emission at anealing tempertures of 900°C
Thermal activation of a-SiC
0 200 400 600 800 1000
Tb3+
Dy3+
Eu3+
Pe
ak In
ten
sitie
s [a
.u.]
Annealing Temperature [°C]
( )as grown
exponential growth with anealing temperature there is no saturation up to 1000°C there is an optimal anealing temperature for the Tb3+ emission in a-SiC
Thermal activation of a-(SiC)x(AlN)1-x
Thermal activation of a-(SiC)0.83(AlN)0.17:Tb3+
Summary
Wide-bandgap semiconductors
Rare earth doping
bandgap engineering
First results on a-(SiC)x(AlN)1-x thin films
HRTEM investigations
bandgap engineering of a-(SiC)x(AlN)1-x
Cathodoluminescense
optical emission of a-(SiC)x(AlN)1-x
thermal activation of rare earth emission
Conferences/Publications: IMRC 2009 in Cancun, Mexico (invited talk) ICSCRM´2009 in Nuremberg, Germany Five publications in International Journals
Acknowledgements
Materials Department, University of Erlangen, Germany
Prof. Dr. Winnacker
Prof. Dr. H. P. Strunk
Catholic University of Lima, Peru (PUCP)
Prof. F. De Zela
Andrés Guerra, Gonzalo Galvez, Oliver Erlenbach (PhD)
Liz Montañez, Katia Zegarra, (Licenciatura)
This research work is supported by the
• Pontificia Universidad Católica del Peru (PUCP)• Deutsche Forschungsgemeinschaft (DFG) and the• German Service of Academic Interchange (DAAD)
Wide bandgap semiconductors
From Steckl MRS Bull. 24, p. 33 (1999)
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