Unit 1 Lect-5Material Science SRM 1st year Unit 1 LECTURE NOTES-6

8/18/2019 Unit 1 Lect-5Material Science SRM 1st year Unit 1 LECTURE NOTES-6

1/54

LECTURE 5

PHOTONIC MATERIALS:

1.LIGHT EMITTING DIODE (LED)

2.LIQUID CRYSTAL DISPLAY (LCD)

3.PHOTO CONDUCTING MATERIALS

15PY102L UNIT 1 LECTURE 5


2/54

What is LED?

• S e m i c

! " # c $

% &

' % i ! ( ) #

* + i $ ,

$ + i ( -

$ .

• $ +

i ( - $ .

LED are semiconductor p-n junctions that under forward bias

conditions can emit radiation by electroluminescence in the UV, visible

or infrared regions of the electromagnetic spectrum. he !uanta of

light energy released is appro"imately proportional to the band gap of

the semiconductor.


3/54

3

• A light emitting i!e "LED# is essentiall$ a PN %&n'ti!n

!(t!)semi'!n&'t!* that emits a m!n!'h*!mati' "single

'!l!*# light +hen !(e*ate in a ,!*+a* -iase i*e'ti!n.

•LEDs '!n/e*t ele't*i'al ene*g$ int! light ene*g$. The$ a*e

,*e&entl$ &se as (il!t lights in ele't*!ni' a((lian'es t!

ini'ate +hethe* the 'i*'&it is 'l!se !* n!t.


4/54

P-$!ic m*$e%i*+& / Li-$ Emi$$i! Di"e&

LED "Light Emitting Di!e# is a semi'!n&'t!* ()n %&n'ti!ni!e +hi'h '!n/e*ts ele't*i'al ene*g$ t! light ene*g$ &ne*

,!*+a* -iasing.

P%i!ci0+e

The i!e is ,!*+a* -iase. D&e t! ,!*+a* -ias thema%!*it$ 'a**ie*s ,*!m n4 an (4 *egi!ns '*!ss the %&n'ti!n

an -e'!me min!*it$ 'a**ie*s in the !the* %&n'ti!n "i.e.#

Ele't*!ns +hi'h a*e ma%!*it$ 'a**ie*s in n4 *egi!n '*!ss the

%&n'ti!n an g! t! (4 *egi!n an -e'!me min!*it$ 'a**ie*s in

()*egi!n

imila*l$ h!les +hi'h a*e ma%!*it$ 'a**ies in (4 *egi!n

'*!ss the %&n'ti!n an g! t! n4 *egi!n an -e'!me min!*it$

'a**ie*s in n4 *egi!n an this (hen!men!n is 'alle minority

carrier injection. 15PY102L UNIT 1 LECTURE 5


5/54

R*"i*$ie %ecm'i!*$i!

N!+ i, the -iasing /!ltage is ,&*the* in'*ease these

e6'ess min!*it$ 'a**ie*s i,,&se a+a$ ,*!m the %&n'ti!n an

the$ i*e'tl$ *e'!m-ine +ith the ma%!*it$ 'a**ie*s. "i.e.# the

ele't*!ns +hi'h a*e e6'ess min!*it$ 'a**ie*s in ()*egi!n

*e'!m-ine +ith the h!les +hi'h a*e the ma%!*it$ 'a**ie*s in

(4 *egi!n an emit light. imila*l$ the h!les +hi'h a*e

e6'ess min!*it$ 'a**ie*s in n4 *egi!n *e'!m-ine +ith the

ele't*!ns +hi'h a*e ma%!*it$ 'a**ie*s in n4 *egi!n an emit

light. 15PY102L UNIT 1 LECTURE 5


6/54

Th&s *aiati/e *e'!m-inati!n e/ents lea t! (h!t!nemissi!n. The n&m-e* !, *aiati/e *e'!m-inati!n is

(*!(!*ti!nal t! the 'a**ie* in%e'ti!n *ate an hen'e t! the

t!tal '&**ent ,l!+ing th*!&gh the e/i'e as gi/en -$

−

= 1exp0

kT

eV I I

β

+he*e I0 ) the sat&*ati!n '&**ent 7 8) the ,!*+a* -ias

/!ltage7 9 ) the :!lt;mann '!nstant 7 β )/a*ies ,*!m 1 an 2e(ening !n the semi'!n&'t!* an tem(e*at&*e.

The !(ti'al (h!t!n emitte &e t! *aiati/e *e'!m-inati!n

has the ene*g$ /e*$ 'l!se t! the -anga( ene*g$ Eg an

,*e&en'$ !, the emitte (h!t!n is gi/en -$15PY102L UNIT 1 LECTURE 5


7/54


8/54


9/54

L#mi!e&ce!ce i& $-e 0%ce&& 'e-i!" +i-$ emi&&i!

• L&mines'en'e is a te*m &se t! es'*i-e theemissi!n !, *aiati!n ,*!m a s!li +hen thes!li is s&((lie +ith s!me ,!*m !, ene*g$.

•Ele't*!l&mines'en'e

e6'itati!n *es&lts,*!m the a((li'ati!n !, an ele't*i' ,iel

• In a ()n %&n'ti!n i!e in%e'ti!nele't*!l&mines'en'e !''&*s *es&lting in light

emissi!n +hen the %&n'ti!n is ,!*+a* -iaseE

kP-n junction

Electrical

Contacts



10/54

LEDs 'an -e esigne as eithe* s&*,a'e !*

ege emitte*s. &*,a'e emitting LEDs 'an -e mae s&'hthat the -!tt!m ege *e,le'ts light -a'9 t!+a*s the t!(

s&*,a'e t! enhan'e the !&t(&t intensit$. The main a/antage

!, ege emitte* LEDs is the emitte *aiati!n is *elati/el$

i*e't.


11/54

Whe*e n1 is the *e,*a'ti/e ine6 !, ai* 1.0

n2 is the *e,*a'ti/e ine6 !, the semi'!n&'t!* @!* g*!&( III semi'!n&'t!* n2 3.5

The*e,!*e θ' 1B

C%i$ic*+ *!+e

The*e,!*e all *a$s !, light st*i9ing the s&*,a'e at an anglee6'eeing 1B s&,,e* t!tal inte*nal *e,le'ti!n an as a *es&lt

m!st !, the emitte light is *e,le'te -a'9 insie the

semi'!n&'t!* '*$stal.



12/54

I!&i"e * Li-$ Emi$$i! Di"e

1. T*ans(a*ent

Plasti' Case

2. Te*minalPins

3. Di!e


13/54

T4 me$-"& #&e" $ %e"#ce %e+ec$i! +&&e& i! LED&



14/54


15/54

M*$e%i*+&

The 'h!i'e !, the mate*ials ,!* an LED is e'ie -$ the

s(e't*al *e&i*ements ,!* a (a*ti'&la* a((li'ati!n. The m!st

'!mm!nl$ &se mate*ials ,!* LEDs a*e aP aAs an thei**elate te*na*$ '!m(!&n a As6 P1)6 The -anga( *aiati!n !, aP aAs an aAsP. aP

+hi'h gi/es a (ea9 at 50 nm is /e*$ 'l!se t! the +a/elength

!, ma6im&m e$e *es(!nse.



16/54

This ma9es aP !ne !, the m!st &se,&l !, all /isi-le

semi'!n&'t!* light s!&*'es sin'e in aiti!n t! g*een light

-!th *e an !the* '!l!&*s 'an -e (*!&'e -$ a((*!(*iate

!(ants.

*e+e!$- %e&0!&e LED

m*$e%i*+&

Material DopantBandgap(eV)

Wavelength( Nm)

Quantumefficiency

( %)

GaPGaPGaP

GaAsAlGa

NZn0 NP

As

2.881.802.251.881.84

430690550660675

0.60.20.10.20.2



17/54

P-$!ic m*$e%i*+& / Li#i" C%,&$*+ Di&0+*, (LCD)

Li&i '*$stals a*e !*gani' '!m(!&ns that ,l!+ li9e a li&i

+hile maintaining a l!ng *ange !*e*liness !, a s!li.

The m!le'&les !, li&i '*$stal '!m(!&n a*e in the ,!*m !, l!ng

'iga* sha(e *!s.



18/54

T,0e& Li#i" C%,&$*+&



19/54

Solid

Liuid cry!tal

“fourth state of atter!

Liuid

"a!

S$*$e& M*$$e%

I&$%0ic"&ni,!*m (*!(e*ties in

all i*e'ti!ns#.

A!i&$%0ic"#$u#% &r'stals

ha(e or#entat#onal or%er



20/54

Li#i" C%,&$*+

T,0e& :ase !n the !*ientati!n !, these *!s>li9e (!la* m!le'&les

the li&i '*$stals a*e 'lassi,ie int! th*ee -asi' t$(es. The$

a*e sme'ti' nemati' an 'hl!este*i'.

(i) Smec$ic

The me'ti' (hase '!nsists !, ,lat la$e*s !, 'iga* sha(e

m!le'&les +ith thei* l!ng a6es !*iente (e*(eni'&la* t! the

(lane !, the la$e*. The m!le'&les +ithin ea'h la$e* *emain

!*iente +ithin ea'h la$e* an ! n!t m!/e -et+een la$e*s.

This m!st !*e*e sme'ti' mes!(hase st*&'t&*al m!el.


21/54

(ii) Nem*$icThe nemati' (hase als! has m!le'&les +ith thei* l!ng

a6es (a*allel t! ea'h !the* -&t the$ a*e se(a*ate int! la$e*s.

In the nemati' mes!(hase +hile the m!le'&les maintain thei*

!*ientati!n the ini/i&al m!le'&les 'an m!/e ,*eel$ &( an

!+n.The nemati' li&i '*$stal m!le'&le '!nsists !, t+!

-en;ene *ings lin9e +ith a 'ent*al g*!&(. A t$(i'al e6am(le is

4-methoxybenzenylidene-4-butylanaline (MBBA). The

nemati' li&i e6hi-its '*$stalline (*!(e*t$ !/e* thetem(e*at&*e *ange 20BC t! FGBC.



22/54

Neat#)* +e)t#) , &holester#)

An#sotrp#) su-stan)es a' o throuh one or

se(eral "#$u#% &r'stal Phases

Li#i" C%,&$*+ P-*&e&


http://en.wikipedia.org/wiki/File:LiquidCrystal-MesogenOrder-ChiralPhases.jpg


23/54

(iii) C-+e&$e%ic

Chl!este*i' mes!(hase 'an -e e,ine as a s(e'ial t$(e !,

nemati' in +hi'h the thin la$e*s !, m!stl$ (a*allel m!le'&les ha/e

thei* l!ngit&inal a6es t+iste "*!tate# in a%a'ent la$e*s at a

e,inite angle. This is the m!st !*e*e (hase. Ea'h la$e* is

-asi'all$ nemati'.

LIHUID CRYTAL RIENTATIN

In LCD4s t+! (*e,e**e !*ientati!ns !, LC m!le'&les a*e

&se "i#.


24/54

The iele't*i' la$e* nea* the ele't*!es has (*e,e**e

!*ientati!n +hi'h in t&*n aligns LC m!le'&les. The t!( an

-!tt!m iele't*i' la$e*s a*e -$ K0B +ith *es(e't t! !nean!the*.The*e,!*e the i*e'ti!n !, the '*$stal is *!tate K0B

+ith

*es(e't t! the -!tt!m !, the li&i '*$stal. The li&i '*$stal

th&s a'ts li9e a set !, (!la*ise*s +h!se !(ti' a6es a*e (a*allelt! ea'h !the* in the (*esen'e !, ele't*i' ,iel an in '*!sse

(!siti!n in the a-sen'e !, ele't*i' ,iel.


25/54

Linea* P!la*i;e LightLinea* P!la*i;e Light

• Light &s&all$ /i-*ates in all

i*e'ti!n

• A linea* (!la*i;e light limit

the /i-*ati!n t! !nei*e'ti!n

• It a-s!*-s the '!m(!nent

!, light that /i-*ate in all

!the* i*e'ti!n.

• LCD *e&i*e light t! /i-*ate

in !ne i*e'ti!n


26/54

A-!&t Li&i C*$stal

• Li&i '*$stal m!le'&les 'an

m!/e ,*eel$ +hile maintaining

thei* !*ientati!n.

• It align itsel, t! a (!l$imie

,ilm t! the insie !, a (anel

glass.

• When the t+! glass (anels

a*e n!t aligne the li&i

'*$stal t+ists a''!*ingl$.

• The li&i '*$stal +ill als!

align t! ele't*i' ,iel.


27/54

Eec$ e+ec$%ic ie+"

The ,&namental (*!(e*t$ !, LCDs that ma9es them &se,&l as

is(la$ e/i'e is that the$ a*e sensiti/e t! an e6te*nal ele't*i'

,iel.

The nemati' li&i '*$stal ,ins its a((li'ati!ns in'*easingl$ in

ele't*!)!(ti' e/i'es sin'e thei* m!le'&les 'an -e aligne -$

ele't*i' an magneti' ,iels t! (*!&'e s&,,i'ient 'hange in thei*

!(ti'al (*!(e*ties.Li&i '*$stal m!le'&les *!tate as a *es&lt !, e6te*nal ele't*i'

,iel. The -eha/i!&* !, initiall$ !*e*e li&i '*$stal mate*ial &e

t! in'*ease in ele't*i' ,iel.



28/54

6e-*i#% LC m+ec#+e& i! *! e+ec$%ic ie+"



29/54

The !*ientati!n !, the LC m!le'&les (a*allel t! the glass

(lates is a'hie/e -$ the e(!siti!n !, a la$e* !, iele't*i'

!/e* the t*ans(a*ent ele't*!es.

The iele't*i' la$e* nea* the ele't*!es has (*e,e**e

!*ientati!n +hi'h in t&*n aligns LC m!le'&les. The t!( an

-!tt!m iele't*i' la$e*s a*e -$ K0B +ith *es(e't t! !nean!the*. The*e,!*e the i*e'ti!n !, the '*$stal is *!tate K0B

+ith *es(e't t! the -!tt!m !, the li&i '*$stal.

The li&i '*$stal th&s a'ts li9e a set !, (!la*ise*s +h!se!(ti' a6es a*e (a*allel t! ea'h !the* in the (*esen'e !,

ele't*i' ,iel an in '*!sse (!siti!n in the a-sen'e !, ele't*i'

,iel.



30/54

Let E4 -e the ele't*i' ,iel a((lie in a i*e'ti!n (e*(eni'&la*

t! the li&i '*$stal s!li inte*,a'e. Als! let E'4 -e the ele't*i',iel st*ength at +hi'h LC m!le'&les 'hange ,*!m h!m!gene!&s

!*e* t! a h!me!t*!(i' t$(e.

When EE' the !*e*ing e6ists@ig)aA-!/eJ. I, EE' the li&i

'*$stal m!le'&les a+a$ ,*!m the ele't*!e -egins align al!ng the,iel i*e'ti!n as in @ig)-A-!/eJ. When EMME' then m!st !, the

m!le'&les align al!ng the ,iel i*e'ti!n as in @ig)'A-!/eJ.

LCD ce++ c!&$%#c$i!



31/54

The m!st im(!*tant st*&'t&*e !, t+iste nemati'

mes!(hase li&i '*$stal 'ell. It '!nsists !, a thin la$e* !,LC mate*ial -et+een t+! glass (lates that a*e ,&se

t!gethe*. The thi'9ness !, the LC is 10 t! 25 m. The t+!

glass (lates ha/e t*ans(a*ent ele't*!es !n thei* insie

,a'es mae !, '!n&'ting mate*ial ini&m tin !6ie.



32/54


33/54

T4i&$e" Nem*$ic (TN) Di&0+*,

• Is the m!st '!mm!n LCD Dis(la$.

• The t+! alignments la$e* ,!* the li&i '*$stal

mate*ial a*e !*th!g!nal.

• The light ente*ing the (!la*i;e (anel *!tates -$ the

t+ist in the li&i '*$stal an all!+ing it t! (ass

th*!&gh the se'!n (!la*i;e


34/54

T4i&$e" Nem*$ic (TN) Di&0+*,

• The ele't*i' ,iel is a((lie

> The li&i '*$stal l!ses its t+ist.

> Alight t! the ele't*i' ,iel. > P*e/ents the *!tati!n !, the (!la*i;e light

> The se'!n (!la*i;e* a-s!*-s the light.

• The a((lie /!ltage '!nt*!l the a-s!*-e an t*ansmitte

light 15PY102L UNIT 1 LECTURE 5


35/54

The +!*9ing !, LC is(la$ e/i'e is sh!+n in a-!/e ,ig.

The 'ell is assem-le s! that LC m!le'&les &ne*g!

K0B t+ist ,*!m the t!( (late t! the -!tt!m (late. The 'ell is

san+i'he -et+een t+! (!la*ise*s +ith thei* (!la*isati!n

i*e'ti!n is (a*allel t! the LC i*e'ti!n !, ea'h (late.

The in'ient &n(!la*ise light !n the 'ell is (!la*ise

linea*l$ as ini'ate an &ne*g!es K0B *!tati!n as it (asses

th*!&gh the LC -e,!*e e6iting the -!tt!m !, the (!la*ise*. In

this m!e !, !(e*ati!n ,*e&entl$ &se in LCDs the 'ell is

t*ansmissi/e in the a-sen'e !, ele't*i' ,iel.



36/54

When /!ltage is a((lie t! the ele't*!es the LC

m!le'&les +ill align +ith ,iel. N!+ the in'ient light! n!t &ne*g! *!tati!n in (!la*i;ati!n i*e'ti!n &e

t! li&i '*$stal an the*e,!*e a-s!*-e -$ the e6it

(!la*i;e*.

Th&s the t+iste nemati' li&i '*$stal 'ell is !(a&ein *i/en state an t*ansmissi/e in n!n *i/en state.


37/54

The LC is(la$ e/i'e 'an -e !(e*ate eithe* int*ansmissi!n !* *e,le'ti!n m!e. In the *e,le't!* m!e a

*e,le't!* is (la'e -el!+ the -!tt!m !, the (!la*i;e*. With n!

,iel the*e,!*e the e/i'e *e,le'ts the in'ient light an

a((ea*s -*ight. When the ,iel is a((lie the i*e'ti!n !,

(!la*isati!n !, light t*a/elling a'*!ss the 'ell is n!t *!tate an

'ann!t (ass th*!&gh the se'!n (!la*i;e* an the e/i'e +ill

a((ea* a*9.

Limi$*$i! $4i&$e" !em*$ic "i&0+*,&

"i# 8ie+ing angle is *est*i'te t! ±F5B"ii# Use !, (!la*ise*s *e&'es the ma6im&m am!&nt !, light

that 'an -e *e,le'te.



38/54

S#0e% $4i&$e" !em*$ic "i&0+*,&

The$ a*e -asi'all$ TN is(la$s !nl$ -&t the$ ha/e at+ist !, K0B t! 2G0B ,*!m t!( t! -!tt!m (lates &(e* t+iste

nemati' is(la$s ha/e g*eate* image '!nt*ast an +ie*

*ange !, /ie+ing angles.


39/54

S#No#L$D LD

Demerits Merits

1 &ost #s h#h )opare% to "&/ &ost #s (er' lo.

2. Not su#ta-le for lare area %#spla' +u#ta-le for lare areas %#spla'

3. #h )onsupt#on Poer #ll#atts "o poer )onsupt#on #)roatts

Merits Demerits

4. perat#n teperature #s 0 to 70&. perat#n teperature #s 10& to 47&.

5. esponse t#e #s #n nano se)on%s 109 se)

esponse t#e #s #n #)rose)on%s 106 se)

6. ntens#t' of l#ht )an -e )ontrolle% ntens#t' of l#ht )annot -e )ontrolle%.

7. /#fferent )olour %#spla's are a(a#la-le at lo)ost.

&olour %#spla's #ll not -e a(a#la-le at lo )ost.

Cm0*%i&! 'e$4ee! LED *!" LCD



40/54

PHOTOCONDUCTING MATERIALS

INTRODUCTION

The (h!t!'!n&'ti/e e/i'e is -ase !n the e'*ease

in the *esistan'e !, 'e*tain semi'!n&'t!* mate*ials +hen

the$ a*e e6(!se t! -!th in,*a*e an /isi-le *aiati!n.

* The (h!t!'!n&'ti/it$ is the *es&lt !, 'a**ie* e6'itati!n &e

t! light a-s!*(ti!n an the ,ig&*e !, me*it e(ens !n thelight a-s!*(ti!n e,,i'ien'$. The in'*ease in '!n&'ti/it$ is &e

t! an in'*ease in the n&m-e* !, m!-ile 'ha*ge 'a**ie*s in the

mate*ial.



41/54

Se$c- * 0-$c!"#c$ie "eice



42/54

T


43/54

Let I0 -e the intensit$ !, m!n!'h*!mati' light ,alling

n!*mall$ !nt! the sla-. Then the intensit$ !, t*ansmitte

light I is gi/en -$

I I0 e6( " ):D#.

Whe*e O is the a-s!*(ti!n '!e,,i'ient !, the mate*ial

an D is the thi'9ness !, the sla-.

Let L an : -e the length an -*eath !, the

(h!t!'!n&'ti/e sla- *es(e'ti/el$. Als! let &s ass&me that

the sla- a-s!*-s the enti*e light ,alling !n it.15PY102L UNIT 1 LECTURE 5


44/54

N!+ the light ene*g$ ,alls !n the sam(le (e* se' is gi/en -$

I0 :L

+he*e I0 is the light ene*g$ ,alling (e* se'!n !n &nit a*ea

!, the sla-. The*e,!*e the n&m-e* !, (h!t!ns ,alling !n the

(h!t!'!n&'t!* (e* se'!n hv

BL I 0

=

Let ) -e the &ant&m e,,i'ien'$ !, the a-s!*(ti!n (*!'ess. It

is n!thing -&t the ,*a'ti!n !, in'ient ene*g$ a-s!*-e.

The*e,!*e the n&m-e* !, (h!t!ns a-s!*-e (e* se'!nhv

BL I 0

η =

N!+ the a/e*age gene*ati!n *ate !, 'ha*ge 'a**ie*s is gi/en -$

hvBLD

BL I r g

0η

=hvD

I r g

0η =



45/54

Une* ill&minati!n the '!n&'ti/it$ +ill in'*ease -$ an

am!&nt is

Let Qn an Q P -e the e6'ess ele't*!n an h!le ensit$

(e* &nit /!l&me in the e/i'e. I, ;' is the li,e time !, 'ha*ge'a**ie*sThen the *e'!m-inati!n *ate

At e&ili-*i&m the *e'!m-inati!n *ate gene*ati!n *ate

The*e,!*e Q ( Q n * g ;'We 9n!+ the '!n&'ti/it$ !, a semi '!n&'ting mate*ial is

cc

r

pnr

τ τ

∆=

∆=

he e. pne µ µ σ +=

he e. pne µ µ σ ∆+∆=∆

)( ne he µ µ +∆=

)( er hec g µ µ τ +=15PY102L UNIT 1 LECTURE 5


46/54

When a /!ltage is a((lie t! the '!nta'ts ele't*!ns an

h!les m!/e in !((!site i*e'ti!ns *es&lting in a (h!t!'&**entgi/en -$

V L

BDi σ ∆∆ =

The &ant&m e,,i'ien'$ !, a (h!t!'!n&'t!* e/i'e is

e,ine -$ the te*m (h!t!'!n&'t!* gain . Ph!t!'!n&'ti/e

gain is e,ine as the *ati! !, *ate !, ,l!+ !, ele't*!ns (e*se'!n t! the *ate !, gene*ati!n !, ele't*!n h!le (ai*s +ithin

the e/i'e. pairsholeelectronof generationof Rate

sec / electronsof flowof RateG

−=

:&t *ate !, ,l!+ !, ele't*!ns (e* se'Qie

V )( er L

BDi hec g µ µ τ +=∆


47/54

Rate !, gene*ati!n !, ele't*!n h!le (ai*s * g:LD

BLDr

eiG

g

32∆=

2

3

L

V G

hec µ µ τ +

=

The (h!t!'!n&'ti/e gain 'an -e in'*ease -$

in'*easing the /!ltage 8 an e'*easing the length L !, the

e/i'e.

The (h!t!'!n&'ti/e gain 'an als! -e e,ine as the*ati! !, the min!*it$ 'a**ie*s li,e time an the t*ansit time t.

i.e.

t G c

τ =

cτ



48/54

C!&$%#c$i! 0-$c!"#c$ie "eice

Geme$%, $-e 0-$c!"#c$ie ce++

In a t$(i'al '!nst*&'ti!n !, (h!t!'!n&'ti/e e/i'e thin ,ilm ise(!site !n an ins&lating s&-st*ate. The ele't*!es a*e

,!*me -$ e/a(!*ating metal s&'h as g!l th*!&gh a mas9 t!

gi/e '!m- )li9e (atte*n as sh!+n -el!+.


49/54

The ,!&* mate*ials n!*mall$ em(l!$e in

(h!t!'!n&'ti/e e/i'es a*e Cami&m &l(hie

"C# Cami&m elenie "Ce# lea s&l(hie

"P-# an Thalli&m &l(hie "Tl#.

The ge!met*$ *es&lts in a *elati/el$ la*ge a*ea !,

sensiti/e s&*,a'e an a small inte* ele't*!e s(a'ing.

This hel(s the e/i'e t! (*!/ie high sensiti/it$.



50/54

When the e/i'e &ne* ,!*+a* -ias is ill&minate +ith light

ele't*!n>h!le (ai*s a*e gene*ate. The ele't*!n)h!le (ai*s

gene*ate m!/e in !((!site i*e'ti!ns. This *es&lts in a

(h!t!'&**ent.

The (h!t!'!n&'ti/e 'ell has /e*$ high *esistan'e in a*9

'alle a*9 *esistan'e. When ill&minate the *esistan'e ,alls.

The s(e't*al *es(!nse !, C 'ell is simila* t! that !, the h&mane$e. The ill&minati!n 'ha*a'te*isti's !, the 'ell is sh!+n in -el!+

,ig.



51/54

P-$c!"#c$% i! ci%c#i$ S0ec$%*+ %e&0!&e C"S ce++



52/54

De&i%e" c-*%*c$e%i&$ic& 0-$c!"#c$ie m*$e%i*+&The$ a*e

i#


53/54

(ii) Le*" +i"e (P'S)

It has s(e't*al Res(!nsi/it$ "Rati! !, (h!t!ns in'ient t! '&**ent

(*!&'e# ,*!m 1 t! 3.F Sm an hen'e /e*$ m&'h s&ita-le ,!* ,a-*i'atingnea*)in,*a*e ete't!*s. It has ma6im&m sensiti/it$ in the *egi!n !, 2 Sm +ith

t$(i'al *es(!nse time a-!&t 200 Ss.

(iii) I!"i#m *!$im!i"e (I!S')

These ete't!*s ha/e +a/elength *es(!nse e6tening !&t t! G Sm ane6hi-it *es(!nse times !, a*!&n 50 ns.

(i) Me%c#%, c*"mi#m $e++#%i"e (H7C"187 Te)

This is an all!$ '!m(!se !, the semi)metal


54/54

APPLICATIONS O9 PHOTOCONDUCTIITY DEICES

The$ a*e

Light mete*s

In,*a*e ete't!*s

T8 'ame*as

8!ltage *eg&lat!*

Rela$s an

Dete'ting shi(s an ai* '*a,ts

Date post:	07-Jul-2018
Category:	Documents
Upload:	ece-a-srm-vdp
View:	230 times
Download:	1 times

Unit 1 Lect-5Material Science SRM 1st year Unit 1 LECTURE NOTES-6

Documents