8/18/2019 ieee paper of mesfet

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I EEE TR A N SA C TIO N S

ON

ELECTRON DFV1CF.S.

VOL

37. N O

6 J U N E

I Y W 1533

Fig. 2. A radiation pattern of the plasma from a tired cell is shown, su-

perimposed nn the usual optical pattern. The emitt er injection current

is

10 mA through 500-R load from 5

V .

The plasma area is partly covered

by the metallized middle row. so that the recombination radiation image

is observed

as

separated by this metallization line. The shift pulsewidth

and also the exposut-e time are 40 ps and the integration is 60

s.

Fig. 3 . Consecutive patterns of the emission by delaying the sampling sig-

nal. The delay is changed by 20-ps interval. A unit transfer occurs cvery

4 0 ps A transient and stable plasma states are alternativcly displayed.

It implies that a timing analysis of digital circuit

is

po\sihlc.

[ l ] A . G . Chynoweth and

K .

G. McK ay. Photon emission from ava-

lanche breakdown

in

silicon. P h ~ s .

ei, .

. v o l . 102. no

2 ,

pp.

369-

376, 1956.

[2]

C .

Hu. S . C. Tam. F-C. Hsu ,

P - K . K O ,

T-Y. C han. and

K .

W . Terril.

Hot-electron-induced MOSF ET degra datio n~m odel. monitor. and

improvenicnt. / € E €

7rwi s Elcctrori De\ ,ic.rs.

vol. ED-32. no.

2. pp.

375-385, 1985.

131 T . Tsuchiya and S. Nakajiina. Emission mechanism and hi ad ep en -

dent emission cfhciency of photons induced by drain avalanche in Si

MOSFETs.

l E E E Trtrris.

Electroti

Dci.ic ,.\.

vol. ED-32. n o . 2 pp.

405-412. 1985.

4 N Khurana and C-L. Chang. Analysis of product hot electron prob-

lems by gated emission microscope.

i n

24th A n n .

P r o , .

/ E E E / R P S .

pp. 189-194. 1986.

[SI N. Khurana, Pulsed infrared microscopy fo r debugging

i n

latch-up

on CM OS product\. in A m i .

Proc. IEEEI IRPS .

pp. 122-117. 1984.

161

S-C. Lim and E - G . Tan, Detection of junction spiking and

i t s

in-

duced latch-up by emission microscopy, i n

A I I H . Proc,.

/ E E E / / R P S .

pp. 119-125. 1988.

[7] M. Sakaue. T. Tamaina, and Y. Mizushima, Unidirectional transfer

properties of plasma-coupled shift register.

/EEE Trans. Electrotl

De1ice.s.

v o l .

ED-29. no. 8 , pp.

1276-1283,

1982.

[SI T . Tamarna and N. Kuji. Auto-calibrated potential m ap drawing

equipment and its application to characterization of plasma-coupled de-

vices. / E E E

7rcr i.s.

Elec t ron Dc1,icxs. vol. ED-33, no. 2. p p . 192-

197. 1986.

Gallium Arsenide Photo-MESFET's

B .

LAKSHMI, K . CHALAPATI . A.

K .

SRIVASTAVA.

B . M. ARORA, S . SUBRAMANIAN, A N D

D . K . SHARMA

Abstract-Response of norma ll)

off

GaAs photo-MESF ET's has been

investigated in two modes: i) the normal mode in which the photon

energy is greater than the bandgap and the light intensity is sufficient

to

bias the device abme turn-on threshold, and i i) the wbthreshold

mode with subbandgap photon energy i l lumination. In the second

mode, the tranGstor operates b j internal photoemission from metal

gate to the semiconductor. In the n ormal mode , the square root of the

drain photocurrent \ar ks

as

logarithm of the incident light intensity.

The device characteristics for subbandgap i l lumination have been an a-

ly7ed for the first time and we show that the photocurrent varies lin-

early with light intensity in this mode.

I . I N T R O D L ~ C I I O N

Re c e n t l y , u l t r a f a s t p h o t o r e sp o n se o f G a A s M E SFE T ' s . a l so

c a l l e d O PFE T ' s , h a s a l so b e e n d e m o n s t r a t e d

[ I ] .

T h e se d e v i c e s

are capab le o f de tec t ing l igh t pulses of 100-ps dura t ion wi th a

2-GHz

repetition rate [21, [31. Su g e t a er

a l .

[2] a l so e x p l o r e d t h e

m e c h a n i sm o f p h o t o d e t e c t io n by M E SF E T ' s . T h e y f o u n d t ha t t he

M E SFE T f ir st a c t s as a p h o t o d i o d e , a n d t h e n t h e F E T a m p l i f i c at i o n

takes p lace . An a l te rna t ive exp lanat ion , based on a d i rec t op t ica l ly

induced modula t ion of d e p l e t i o n l a y e r , h a s b e e n p r o p o se d b y T .

U m e d a et al . 141. Since Scho t tky-bar r ie r s t ruc tu re i s a major i ty -

car r ie r dev ice . i t can have tu rn -on and tu rn -of f t imes as smal l as a

f e w p i c o se c o n d s 151 a n d t h e r ef o r e M E SF E T ' s c o u l d b e f a b ri c a t e d

to detec t ex t remely shor t l igh t pu lses .

In th is b r ie f . pho todetec t ion response measurements were per -

f o r n i e d o n G a A s M E SFE T d e v i c e s . i n c l u d i n g t h e i r r e sp o n se to

p h o t on e n e r g i e s sm a l l e r t h a n t h e b a n d g a p o f G a A s . Fo r t h e p h o t o n

e n e r g i e s b e t w e e n t h e Sc h o t t k y - b a r r i e r h e i gh t a n d t h e b a n d g a p e n -

e r g y (0.85-1.4 e V ) it is the in terna l pho toemission p rocess which

g ives r i se to pho tocur ren t . Th is cu r ren t is in turn, amplif ied by the

FE T . A se l f - c o n s i s t e n t m o d e l u s i n g m e a su r e d p a r a m e t e r s is pre-

sen ted to exp la in the resu l ts . The spec t ra l r esponse in the subband-

gap reg ion shows the behav i o r p red ic ted by the Fowl er theory 161

and our resu l ts conf i rm the mechan ism proposed by Sugeta et a / .

11. E X P E R I M E N T A L

N o m i a l l y off G a A s M E SFE T d e v i c e s w e r e f a b r i c a t e d o n se m i -

insu la t ing GaAs subst ra tes ion- implan ted wi th s i l icon using s tan-

d a r d p r o c e ss i n g s t e p s . T h e c u r r e n t - v o lt a g e b e h a v i o r o f t h e M E S-

FET 's wa s invcst iga tcd under f ron t i l luminat ion . For pho ton

Manuscript received May 23.

1989.

revised December 15. 1989. The

review

of

this brief

wa,

arranged by Associate Editor

G .

Craford.

B. Lakshmi and K. Chalapati are with SAMEER, Indian Institute of

Technology Campus. Bombay 400076, India.

A . K . Srivastava, B . M. A rora, S . Subramanian, and D.

K .

Sharma are

with the Tata Institute of Fundamental Research, Bombay 400005. In dia.

IEEE Log Number 9034392.

0018-9383/90/0600-1533 01OO 1990 I E E E

Authorized licensed use limited to: INDIAN INSTITUTE OF TECHNOLOGY BOMBAY. Downloaded on January 24, 2009 at 04:07 from IEEE Xplore. Restrictions apply.

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1534

It.F.F, T K A N S A C T I O N S O N

F.I.ECIROK

DF..VICk.:S. VOL.

37. N O . 6 J U N t I 9 4 0

en e rg i e s

hv > E,,

a 2 -m W H e-Ne l a s e r was u s ed . T h c i n t en s it y

of i l luminat ion was var ied by a set of neut ral dens i ty f i l t ers . For

s p ec t ra l r e s p o n s e m eas u rem en t s , l i g h t f ro m a t u n g s t en l am p was

p as s ed t h ro u g h a m o n o ch ro m at o r an d t h en fo cu s ed o n t o t h e g a t e

r eg i o n . F o r p h o t o n en e rg i e s h u < E,, t h e l ig h t b eam w as ch o p p ed

an d t h e p h o t o cu r r en t was m eas u red b y u s i n g a l o ck - i n am p l i f i e r .

C u r r en t -v o l t ag e b eh a v i o r in d a rk was a l s o m eas u red .

111. RESULTSA N D DI SCLI SSI O N

A .

Normal Operation

F i g .

1

s h o ws t y p i ca l l,),5-VDs character i s t i cs of a l arge-area

( 9 0 - p m - l o n g g a t e ) d e v i c e o p e r a t i n g

i n

d a r k . T h e d e v i c e s h o w s

normal ly off b eh av i o r an d o p e ra t e s a s an en h an cem en t -m o d e M E S -

F E T , w i t h a t h r e s h o l d v o l t ag e

V ,

= 100 m V. S i m i l a r ch a rac t e r -

i s t i c s were o b s e rv ed w i t h 2 -p m - l o n g g a t e M E S F E T ' s .

F i g . 2  shows typical

ID,s-VD,s

character i s t i cs

of

a large-area

M E S F E T , wh i ch i s o p e ra t ed w i t h a f l o a t in g g a t e an d l i g h t ex c i ta -

t i o n f ro m a He-Ne l a s e r . D i f fe r en t

IDs-VLls

cu rv es were o b t a i n cd

by redu cing the incident l ight wi th cal ibrated neut ral dens i ty f i l t ers .

Character i s t i cs in F i g . 2  r e s em b l e t h o s e i n F i g . I . with the gate

b eco m i n g fo rward -b i a s ed b y l i g h t , l i k e i n S ch o t t k y -b a r r i e r s o l a r

cel l wi th

wh ere

I yc

i s the short -ci rcui t current proport ional to the incident

l ight in tens i ty , lo s the dark saturat ion current . and

n

i s the ideal i ty

f ac t o r o f t h e S ch o tt k y b a r r i e r . T h e v a l u e of

n

was m eas u red t o b e

1.27

f ro m d a rk

I-V

character i s t i cs . By varying the in tens i ty of

il

l u m i n a t i o n , t h e o p en -c i r cu i t v o l t ag e d ev e l o p ed

on

t h e g a t e ch an g es

an d h en ce a f am i l y o f I DS - VDs u rv es were o b t a i n ed . I n t h e s q u a re

l aw r eg i m e , w i t h

VGs

>>

V , .

t h e d r a i n cu r r en t d ep en d s o n t h e

incident l ight power P as fo l l o ws :

w h e r e

q

i s the quantu m eff iciency and

hv

i s t he p h o t o n en e rg y . F ig .

3 

sho ws a p lo t of versus log of normal ized incident pow er .

T h e d a t a a r e i n s a t is f ac to ry ag reem en t w i t h t h e ab o v e r e l a t i o n sh i p

(2 ) . T h e s p ec t r a l r e s p o n s e o f t h e d ev i ce i s s h o wn

i n

F i g .

4.  A

s h a rp

r i se in respons iv i ty at

-

. 4 - eV p h o t o n en e rg y i n d i ca t e s t h e o n s e t

of the band-to-band absorpt ion . In addi t ion to the h igh respons iv i ty

a t p h o to n e n e rg i e s hv >

1.4

eV , t h e d ev i ce s h o ws s i g n i f ican t r e -

s p o n s e a t s u b b an d g ap en e rg i e s .

B. Subthreshold Subbundgap Operution

Th e inset in F i g . 4 s h o ws t h e d ev i ce r e s p o n s e a t p h o to n en e rg i e s

h u <

1 . 4 e V e x t e n d i n g d o w n t o

-0.8

eV. Ga As d o es n o t hav e

s igni f icant absorp t ion at these photon en ergies

(0 .8-1 .3

e V ) t o g i v e

t h e o b s e rved p h o t o res p o n s e f ro m a

-

. 4 -p in- th ick act ive l ayer in

t h e d ev i ce . T h e p h o t o res p o n s e can b e cau s ed b y t h e i n t e rn a l p h o -

t o em i s s i o n o f e l ec tro n s f ro m t h e g a t e m e t a l i n t o th e ch an n e l . T o

inves t igate the mechanism

of

t h e s u b b an d g ap p h o t o rcs p o n s e . t h e

relat ionship between the incident l ight in tens i ty and the drain cur-

r en t n eed s t o b e e s t ab l is h ed . Un d er weak i l l u m in a t i o n , t h e Vc;sd e -

v e l o p ed i s m u ch s m a l l e r t h an

V ,

and the device oper ates in the

subthre shold condi t ion . A plo t of

I,,\

versus

Vc;,5

character i s t i cs of

t h e d ev i ce o p e ra t i n g i n d a rk a t l o w g a t e b i a s Vc;,5

<

100 m V )

on

a semi lo g scale g ives a s t raight l ine indicat ing that i n t h e s u b t h res h -

old region IDS varies exponent ial ly wi th Vc;,s

3 )

wh ere Vo

I S

found to b e 4 0 m V . Un d e r i l lu m i n a t io n w i t h hv < E,,

the open-ci rcui t vol tage at the gate can s t i l l be expressed by I )

F r o m I ) and

(3)

we g e t

,111

q

4)

VDS V )

Fig.

I

/ i l , - V , 5 characteristics

ot

GaAs MESFET operating in dark

He

Ne

Loser

Illurninallon

.? 1 0 2 0 3 04 0 5 0 6 7 8

09

V D ~

VOLTS)

Fig. 

2 .

Opcn-gate MESFET characteristics with

He-Ne

laser illumina-

tion

Illumination

LG 90prn

6 7

Fig. 

3 .

/i,.5-light intensity characteristics

of

MESFET for

He-Ne

illumi-

nation.

For I S c

8/18/2019 ieee paper of mesfet

3/3

PHOTON ENERGY eV)

Fig. 4. Spectral response of

GaAs

MESFET.

1 1 1

1 8 1 1

0 IO 20

30 40 5 0

60

70

8

90

Fig. 5 . AC photocurrent f , , , , - f , , characteristics o f G a A s MESFET at a

wavelength of I

pili.

PHOTON ENERGY eV)

Fig.

6.

(Yield) '

versus photon energy characteristics for G a A \ MESFET

in the subbandgap region.

Th e ac pho tocur ren t a t the d ra in i s therefo re g ive n by

153s

w h e r e f i s r e la ted to inc iden t chopped l igh t pow er as

- I

I, ( .

11

v

Fi g . 

5

sho ws a p lo t o f versus i5 t I -Km w a v e l e n g t h . A s a n -

t ic ipa ted f rom

(6).

a l inear re la t ionsh ip is observed be tween i/),sn d

is . .h e r a t i o f/),s/[,(. i s constan t and expre sses the cur ren t ga in in

the sub th resho ld reg ion . T he va lue of cur ren t ga in i s found to be 7

in our dev ices .

I n o r d e r t o su b s t a n t i a t e t h e i n t e r na l o h o t o e m i ss i o n n a t u r e

of

t h e

p h o t o r e sp o n se i n t h e su b b a n d g a p r e g i m e . w e h a v e p l o t t e d t h e

sq u a r e r o o t o f t h e d r a i n c u r r e n t p e r i n c i de n t p h o t o n o r t h e y i e l d Y

a s a f u n c t i o n o f t h e p h o t on e n e r g y . T h e e x p e r i m en t a l c u r v e i s sh o w n

in F i g . 6. 

A

l inear re la t ionsh ip is seen over a wide energy range

h u

> 48. W e o b t a i n a v a l ue

of G -

0.87

c V .

w h i c h is

in

g o o d a g r e e -

ment wi th the Ti-Ga As Scho t tk y-bar r ie r he igh t 161.

I V .

C O N C L U S I O N

A normal ly off M E S F E T c a n

be

u se d f o r d e t e c t i n g l i g h t o f e n -

ergy i ) above the bandgap of the semiconducto r by hand- to -hand

e x c i t a t i o n s a n d i i ) b e l o w t h e se m i c o n d u c t o r b a n d g a p b y i n t e rn a l

p h o t o e m i ss i o n . T h e l o w e r l i m i t o f t h e p h o t o n e n e r g y t h a t c a n b e

detec ted in the la t te r cas e

is

g i v e n b y t h e g a t e Sc h o t t k y - b a r r i e r

h e i g h t . I n b o t h c a se s , t h e p h o t o r e sp o n se s c a n b e e x p l a i n e d b y a

model

in

w h i c h t h e M E SF E T g a t e Sc h o t t k y b a r r ie r a c t s l i k e a p h o -

tod iode and develops a pho tovo l tage under i l luminat ion , which , in

t u r n . c h a n g e s t h e d r a i n c u r r e n t . T h e r e sp o n se c u r r e n t i s a m p l i -

t ied by the F ET t ransis to r ac t ion . In the nomial m ode

of

o p e r a t i o n ,

var ies logar i thmica l ly wi th the l igh t in tensi ty . W e have

sh o w n t h a t i n t h e su b t h r e sh o l d - m o d e o p e r a t i o n t h e d r a i n c u r r e n t

v a r ie s l i n e a r ly w i t h t h e l i g h t i n t e n si t y . T h e p h o t o - M E SFE T t h u s

p r o v i d e s m e a n s f o r l i g h t d e t e c t i o n o v e r a w i d e e n e r g y r a n g e w i t h

a m p l i fi c a t io n . S i n c c M E SF E T ' s a r e m a j o ri t y -c a r ri e r d e v i c e s . t h e y

a l so o t f e r t h e a d v a n t a g e o f h i g h sp e e d .

A C K N O W L . ~ , D G M E N ~ '

a s s i st a n c e i n t h e f a b r ic a t i on o f M E SF E T ' s .

T h e a u t h o r s w i sh t o t h a n k P . P. Su r a t k a r a n d

V .

T . K a r u l ka r f o r

[ I ] J . C. Campbell. Photo-transistora. in Ser,iic.orit/rc[.,ors t r r i d

Semi -

/ w r t r / s .

vol. 2 2 D .

W .

T. Tsan g. Ed

New

York. NY : Academic Press.

1985.

121 T. Sugeta and Y . Mirushima. High speed photoresponse mechanism

of a GaAs

MESFET.

J t r p t r ~ i

. A ~ / J / .

h\ s . .

vol.

19

p .

L27.

1980.

131 J . C . Gamniel and J . M. Ballantyne. The OPFET: A

new

high speed

optical detector. in

l E D M

Proc. . pp. 120-123, 1980.

141

T . Umeda and Y . Cho. Etfect oi ncident light illumination shape o n

responsivity o f G a A s MESFET photodetector, trptrti

J .

App l .

P/i .\.

pp. L367TL364. 1985.

I S ] A . McCowen. S . B . N Shaari. and K . Board, Transient analykis o f

Schottky harrier diode.

/ / I . s I .

Elrc .. E r ~ ~ y . .t. 1 vol. 135. p . 71.

1988.

161 S. M. Sze . Ph .sic..\ ( f S~,r , i ic .o ir t / rcc .ro , . D o V c r s . New York. NY:

Wiley.

1969.

ch .

8 .

On

the Calculation of Specific Contact Resistivity on

( 100

Si

KWOK

K .

NG A NI ) RUICHEN LIU

Abstract-In order to design suhm icromet er Si MOSFET's properly,

the

specific

contact resistivity p , has to he controlled. The p ,

is

known

Manuscript received April 24. 1989: revised January 4. 1990. The re-

The authors are w i t h AT T Bell Laboratories. Murray Hil l , NJ 07974.

IEEE Log Number

903.5

180.

view of this brief was arranged by Associate Editor K . C. S araswat.

Authorized licensed use limited to: INDIAN INSTITUTE OF TECHNOLOGY BOMBAY Downloaded on January 24 2009 at 04:07 from IEEE Xplore Restrictions apply