A MT Ch01 Introduction & Crystals

8/13/2019 A MT Ch01 Introduction & Crystals

1/14

Chapter1page1

MicroelectronicsTechnology

E.F.Schubert2012,allrightsreserved

RensselaerPolytechnicInstituteTroy,NewYork

SolidStateDevices

Examplesare:o

Field

effect

transistors

o Bipolartransistorso LEDs

oLasers

o Photodetectorso Solarcells


2/14

S

T

everalimpo

o Transo Geneo Reco

ransportof

o TransDiffu

>0K,

o Trans

moti

Trans

rtantphysic

portofchar

ationofch

binationo

electrons

port due t

ion isther

whenthese

Synonyms

motion;B

Diffusion

performe

DiffusionNetdiffusi

Netdiffusi

portdue t

nofcharge

The direc

particles

electricfi

Negative

Cha

portofcarralmechanis

gecarriers(

rgecarriers

charge

car

thermal e

ndommov

particlesh

for Diffus

ownianmo

or therm

byRobert

esultsin

ca

onoccursa

onoccursa

anelectri

particlesc

tion of car

nd is dire

ld

lectronsdri

pter1page2

ersbydiffumsdetermi

e.g.electro

iers

nergy of c

ementofp

veatherm

ion: Therm

tion

l motion

BrownB

riertransp

longtheco

longthepo

field D

ausedbyan

rier drift d

ted either

ftagainst

t

sionanddrnethebeha

s)

rriers

articles(e.g

alenergygr

al motion;

was first

rownianm

rtifthere

i

centration

itivexdire

rift.What i

electricfiel

epends on

along or a

edirection

iftviorofchar

iffusion. W

.electrons)

eaterthanz

Random

identified

tion

aconcentr

gradient

tion

sdrift?Dri

d.

the charge

gainst the

ofthe

elect

ecarriers:

hat is diffu

attempera

ero.

otion; Dif

in experi

ationgradie

t is thedir

polarity o

direction o

ricfield

sion?

tures

usive

ents

nt

cted

f the

f the


3/14

R

a

a

I

hmslaw:

o V=Vo R=Ro I=Cu

ecall

nd

nd

sertionof

=urrent I

densurrent

o e=elo n=co v=avo =c

B

ltage

sistance

rrent

q.(2),(3),a

timunit

charge=

J =ty

mentaryc

ncentration

erageveloci

nductivity

Cha

asiclawof

nd(4)into

n

e

e

Area

numbe

arge=1.60

ofelectron

tyofelectr

pter1page3

ransport:IRV

A

lR

AJI

lV E

q.(1)yields

EJ

timeunit

elofumber

timenit

electronof

eJ

21019

C

spercm3

ns

hmslaw

A

l

1

ectrons

vne

s

vn

(1)

(2)

(3)

(4)

(5)

(6)


4/14

erivationo

o Consi

o Neleo Conco Theao Curreo wh

:

derelectron

tronsarein

ntration=

eragevelo

ntdensity:

twastobe

Cha

sinavolu

sidethevol

xA

N

d

ityofcarrie

=

A

eJ

d

shown

pter1page4

eJ

eV=Adx

ume

rsis=

v

xA

Ne

t

d

vn

t

x

d

d

et

x

d

d

v

(7)


5/14

R C

T H R

esistivity=

onductivity

heresistivit

owmanyo

easonfort

o Insulo Metao Semi

o What

o Exam

=

showsala

dersofma

elargevari

tor:

:

onductor:

isthereaso

Chemical

Differenc

Differe

ples:

Metal:

Semicond

Insulator:

Cha

Conducti

rgevariatio

nitude?

tion:Conc

Allelec

Electro

Some

nforthese

atureofel

sintheche

nceinnum

ctor:

pter1page5

ityandresidimension

dimension

ntrationof

tronsareti

nscanfreel

lectronsca

onductivit

mentorco

micalbond

eroffreee

n=1022

n=1015

n=105

stivity)= cm

)= 1

c

electrons:

htlybound

moveabo

freelymo

difference

mpound

lectrons

cm3

020

cm3

cm3

1=Scm

1

toatoms

utthemeta

eaboutthe

?

l

crystal


6/14

C

E

E E

F

Eo

o

E

hemicalmo

amples:

lectroninv

lectronina

reeelectron

lectronsin

Collisions Electrons

lectrostatic

del:Electro

cuum =

solid =

s = fre

= fre

Fr

olids:

withlattice

feelelect

potentialin

Cha

Freeeleisnotlocal

trulyfree

quasifree

etomovea

etomovei

eelectrons

atomsare

rostaticpot

asolid:

pter1page6

ctronsinaizedinapa

lectron

electron

bout(diffus

anelectric

canforma

ossible

ntialofcry

olidrticularche

ion)

field(drift)

electrical

stallattice

icalbond

urrent


7/14

Chapter1page7

o Collisionswithlatticeatomsareminimizedinastrictlyperiodicpotential,thatis,inacrystallinesolid

o Influenceofthelatticeistakenintoaccountbyaneffectivemassofelectrons Example: me = 9.11031kg (freeelectron) me* = 6.11032kg=0.067me (electroninGaAs)

Comparison:Crystallinesolidversusamorphoussolido Highpuritycrystallinesolid=hightechnologysolid

Example:Laser,LED,integratedcircuit,microprocessorchipo Amorphoussolid=lowcostsolid

Example:AmorphousSisolarcell


8/14

T

T

herearedif

o Singlo Poly

o Whico Whico Whic

herearedif

o Simplo Bodyo Faceo Whato

What

erenttypes

crystalline

rystallines

onehasth

onehasth

oneiseasi

erentcryst

ecubiccrys

centeredcu

enteredcu

isthedefini

is

the

defini

Cha

ofsolids:

solids

lids

ehighestm

ehighestel

esttofabric

lstructure

al

biccrystal

iccrystal

tionofthe

tion

of

a

un

pter1page8

Crystals

echanicalst

ctricalcon

ate?

.Common

atticecons

it

cell?

o

rength?

uctivity?

rystalstruc

anta0?

morphous

turesare:

olids


9/14


10/14

o Vapo

o Other

pnjunctio

Heterostr

PhaseEpit

Whyisitc

Chemical Si:

GaGrowtha

growthtec

Cha

ngrowth(e

cturegrow

xy(VPE)is

alledVapor

eactionfor

As:

paratus:Se

nique:Mol

ter1page10

.g.pnjuncti

th(e.g.AlA

acommon

PhaseEpit

thegrowth

SiH4 Si

(CH3)3Ga+

eillustratio

ecularbea

onLED)

/GaAs)

pitaxialgro

xy?

of

+ 2H2

sH3 G

Epitaxy(

wthtechniq

As+3CH4

BE,notdisc

ue

ussedhere)


11/14


12/14

Chapter1page12

Thefourtypesofcrystals

Recallsomechemistryo Atomshaveelectronshellso Acompletelyfilledshellhas2,8,or18electronso Noblegaseshave2(He),10(Ne),18(Ar),,electronso Noblegasesareverystableanddonotreactwithotheratomso Atomshavethetendencytoassumeanoblegaselectronconfiguration

Thereare4mainclassesofcrystals:o Metalliccrystalso Ioniccrystals o Covalentcrystalso Molecularcrystalso Next,wewilldiscussthese4typesofcrystals

1. Metalliccrystals Consideranatomwithonelooselyboundelectron:

o Na (11electrons=2+8+1electron)o Cu (29electrons=2+8+18+1electron)

Inmetalliccrystals,electronsbecomepracticallyfree Thepositivelychargedioncoresareheldtogetherbyaseaofelectrons Metalliccrystalshavehighelectricalconductivity

Example:

Copper,

Cu

o 29protons,29electrons,34neutronso Molarmass=(29+34)g/mol=63g/molo Avogadrosnumber=61023atoms/molo MassdensityofCu=9g/cm3o Atoms per cm3 = 6 1023 atoms/mol (1/63) mol/g 9 g/cm3 =

=8.51022

atoms/cm3

o Electronspercm3=8.51022electrons/cm3

2. Ioniccrystals Twotypesofatomswithlargedifferenceinelectronegativity Oneatomhasalooselyboundelectron One atom has one electronmissing from a noblegas configuration (this is a highly

electronegativeatom) Transferofthelooselyboundelectrontotheelectronegativeatomoccurs


13/14

T

I E

3. Cova

A B

E

hustheioni

ofreeelect

niccrystals

xample:So

o Nao Clo NaCli

lentcrystal

tomswithp

ondsbetwe

xample:

Silio Sihaso Illustr

electr

ccrystalco

rons

areinsulat

iumchlorid

(1

(1

saninsulat

artiallyfille

enlikeato

on,

Si

4outerele

ation belo

onshelland

Cha

sistsofposi

rs

e,NaCl

electrons

electrons

r

outershel

sarealway

trons

shows th

thusisina

ter1page13

tiveandne

2+8+1el

181ele

lsbondbys

scovalent(

t the cent

stableconfi

ativeions

ectron)

tron)

haringelect

.g.O2,N2,

r Si atom

guration

ronstofillt

)

has 8 elect

eoutersh

ons in its

lls

outer


14/14

4. Mole

B E

5. Hybr

cularcryst

ondingforc

olecularcr

aalsbonds

xamples:

o CO2co Snow

dbonding

Group

IV

III

II

I

ls

sareVand

stalsarety

ystals(dryi

crystals

rystals(thi

Group

IV

V

VI

VII

Cha

erWaalsfo

icallymad

ce,lowtem

isnotase

ter1page14

rces(polari

upofmole

peraturesn

arateclassElement

Si

GaAs

ZnS

NaCl

ationforce

culesthata

eeded)

butamixtu

s)

reheldtog

reof2class

c

most

Mo

therbyVa

es)Bond

valent

lycovalent

stlyionic

ionic

der

A MT Ch01 Introduction & Crystals

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