Electrical and photoelectrical properties of crystalline semiconductor-ChVS heterojunction controlled by ChVS modification

Journal of Non-CrystanineSolids 97&98 (1987) 987-990 North-Holland, Amsterdam

987

E L E C T R I C A L AND P H O T O E L E C T R I C A L PROPERTIES OF C R Y S T A L L I N E SEMIC O N D U C T O R - C h V S H E T E R O J U N C T I O N C O N T R O L L E D BY ChvS M O D I F I C A T I O N

Sh. Sh. SARSEMBINOV, O.Yu. PRIKHODKO, S.A. DZAKELOV, V.L. A V E R Y A N O V x

S.Ya. M A K S I M O V A and

Kazakh State University, Alma-Ata, USSR XA.F. Ioffe P h y s i c o - T e c h n i c a l Institute,

Leningrad,

USSR

In the present paper the c u r r e n t - v o l t a g e (in darkness and at light exposure) and c a p a c i t a n c e - v o l t a g e c h a r a c t e r i s t i c s of crystalline S i - m o d i f i e d As2Se 3 h e t e r o s t r u c t u r e s as well as the spectral d i s t r i b u t i o n of their p h o t o c u r r e n t s were studied. Bi and Cu impurities were used as As2Se 3 modifiers. Their c o n c e n t r a t i o n s ranged from O to 15 at%. It is shown that there is a possibility to obtain d e s i r e d parameters and c h a r a c t e r i s tics of these h e t e r o s t r u c t u r e s by m o d i f y i n g c h a l c o g e n i d e vitreous semiconductor and by changing modifier concentration. I. I N T R O D U C T I O N The interest in h e t e r o j u n c t i o n s b e t w e e n crystalline anch chalcogenide vitreous

semiconductors

lity to create p h o t o s e n s i t i v e of these h e t e r o j u n c t i o n s phenomena

(ChVS)

is caused by the possibi-

semiconductor devices on the basis

as well as to investigate contact

in ChVS I'2. It is known that the c h a r a c t e r i s t i c s of

heterostructures

(HS) significantly depend on electrical,

electrical and optical properties of ChVS I-3. Controlling

photothe

properties of these semiconductors by their m o d i f i c a t i o n may provide means of obtaining

HS with d e s i r e d parameters and

characteristics. The aim of this paper is to investigate conductor-modified

ChVS h e t e r o j u n c t i o n s

bility of controlling

the crystalline

semi-

and to reveal the possi-

their properties.

The p-type single crystal

silicon and m o d i f i e d vitreous

conductor As2Se 3 were used in heterostructures.

semi-

Cu and Bi were

chosen as modifier elements since it is known that the introduction of these metals significantly

increases the c o n d u c t i v i t y of

As2Se 3 and decreases the electrical a c t i v a t i o n energy and the optical gap 4'5. Addition of Cu or Bi increases the p h o t o c o n d u c tivity of As2Se 3 too. The arsenic triselenide

films m o d i f i e d with

Cu are p-type while those m o d i f i e d with Bi are n-type at Bi concentrations

exceeding

3 at% 5.

0022-3093/87/$03.50 ©Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

Sh.Sh. Sarserabinov et al. / Electrical and photoelectrical properties

988

2. E X P E R I M E N T A L Heterojunctions

were

As2Se 3 with a metal substrates

were

prepared

on a p-type

preliminarily

Cu and Bi c o n c e n t r a t i o n s The c o n c e n t r a t i o n s X-ray

analyser.

lyses

did not

after

preparing

and after

annealing

of the silicon

triselenlde Aluminium

for ChVS and silicon,

(I-V)

was m e a s u r e d

illumination

using

a Camebax

microscope

of the m o d i f i e d

ana-

films both

at 450 K for 30 min.

single

crystals

was

i0 ~.cm

cm -3

in h e t e r o s t r u c t u r e s

was 0.3

-

materials

and c a p a c i t a n c e - v o l t a g e

characte-

in the dark at room temperature;

at 465 kHz.

and the spectral

out with

method.

from O to 15 at%.

and e l e c t r o n

of 7.1015 layer

Silicon

and indium were used as e l e c t r o d e

of HS were m e a s u r e d

carried

ranged

of

respectively.

The c u r r e n t - v o l t a g e

capacitance

silicon.

atoms were m e a s u r e d

diffraction

concentration

The arsenic

ristics

crystal

in As2Se 3 films

Electron

of RF c o s p u t t e r i n g

from SiO 2 by standard

show any c r y s t a l l i z a t i o n

with the hole

thick.

single

cleaned

of impurity

The r e s i s t i v i t y

0.5 ~ m

by means

the

The I-V c h a r a c t e r i s t i c s

distribution

the use of standard

of p h o t o c u r r e n t

under

were

methods.

3. RESULTS The

investigations

of the d i f f e r e n t modified

types

of c o n d u c t i v i t y

by Bi and Cu the f o r w a r d

are b i a s e d HS.

of I-V c h a r a c t e r i s t i c s

positively

The I-V c h a r a c t e r i s t i c s

A s 2 S e 3 showed power

similar

dependence

and sublinear

behaviour;

dependence

heterostructures

its p h o t o s e n s i t i v i t y

rise when

It was e s t a b l i s h e d fier c o n c e n t r a t i o n

and fill

current.

too.

reaches

of

effect,

Fig.

of

It can be seen

concentration the value

that the As2Se 3 m o d i f i c a t i o n

I~V n

I shows

illumination

with Bi.

the m o d i f i e r

and incre-

of about

104 .

and the m o d i -

lead to a rise of the h e t e r o s t r u c t u r e

such as s h o r t - c i r c u i t

factor,

types

and u n m o d i f i e d

of the h e t e r o s t r u c t u r e

coefficient

increase

the films

for both

on the bias v o l t a g e

in the dark and under

coefficient

The r e c t i f i c a t i o n

parameters,

of the reverse

in spite

triselenide

in r e c t i f i c a t i o n

current

b a s e d Qn As2Se 3 m o d i f i e d

that the r e c t i f i c a t i o n

ases.

to the p-Si

i.e.

that

flows w h e n

of HS with m o d i f i e d

of the forward

the I-V c h a r a c t e r i s t i c s

for arsenic

current

with r e s p e c t

shows

current,

open c i r c i u i t

voltage

Sh.Sh. Sarsembinov et al. / Electrical and photoelectrical properties

Jxlo' < -I .O

989

I I

s

-5

2 1

'4 s' ~

U

f

12

2~ ~ ~

%%

JX10 8 i

/

I

0 .7

VOLTAGE,

V

sensitivity

l

I. um

FIGURE 2 Spectral d i s t r i b u t i o n of photocurrent in the reverse biased HS with As2Se 3 m o d i f i e d with Bi: 1-4 at%, 2-15 at%

The i n v e s t i g a t e d h e t e r o s t r u c t u r e s

photocurrent

I

0.9

WA~LENGTH,

FIGURE I I-V c h a r a c t e r i s t i c s in the dark (1,2) and under illumination (I',2') of HS with As2Se 3 modified with Bi: I-8 at%, 2-15 at%

range of spectral

I

k

are c h a r a c t e r i s e d by a wide

from 0.5 to 1.2 ~ m .

There are two

peaks on the spectral c h a r a c t e r i s t i c s of HS with

As2Se 3 m o d i f i e d with small c o n c e n t r a t i o n s of impurities.

The

positions of the peaks indicate the p a r t i c i p a t i o n of both the crystalline

and the amorphous

ture in photocurrent.

semiconductors of the h e t e r o s t r u c -

While the m o d i f i e r c o n c e n t r a t i o n rises

the position of the p h o t o c u r r e n t peak caused by ChVS is shifted towards the l o n g - w a v e l e n g t h region, current peak caused by Si

that is towards the photo-

(Fig. 2). This d i s p l a c e m e n t

ted with As2Se 3 band gap decrease under modification.

is connecBesides,

it

should be noted that for the h e t e r o s t r u c t u r e s with As2Se 3 modified with large Bi c o n c e n t r a t i o n s

the p h o t o s e n s i t i v i t y

e x p a n d e d towards longer wavelengths.

region is

It is explained by the

decrease e s t a b l i s h e d here of the band gap of As2Se 3 m o d i f i e d with large Bi c o n c e n t r a t i o n s

to values

smaller than that of Si. With

the reverse bias increasing the p h o t o s e n s i t i v i t y

of the hetero-

structures with m o d i f i e d As2Se 3 increases p r o p o r t i o n a l l y over the whole HS p h o t o s e n s i t i v i t y

region,

that is both the h e t e r o s t r u c -

ture's Si and As2Se 3 give an equal p h o t o c u r r e n t rise.

In contrast

with HS with u n m o d i f i e d As2Se 3 a more n o t i c e a b l e rise of photo-

Sh.Sh. Sarsembinov et al. / Electrical and photoelectrical properties

990

current with the increasing reverse bias occurs in the longwavelength

region.

This indicates the expansion of the space

charge region occurs mainly

in Si while the reverse bias incre-

ases.

for h e t e r o j u n c t i o n s between

The latter is typical

silicon

and ChVS 2'3. The c a p a c i t a n c e - v o l t a g e

c h a r a c t e r i s t i c s of the HS with modi-

fied and u n m o d i f i e d As2Se 3 films have sections with linear dependence of I/C 2 on the applied voltage. rojunctions

in the i n v e s t i g a t e d

It indicates that the hete-

structures are abrupt,

the capaci-

tance of h e t e r o j u n c t i o n s under zero bias and the space charge region w i d t h depending on the m o d i f i e r c o n c e n t r a t i o n

in As2Se 3.

4. C O N C L U S I O N So it has been e s t a b l i s h e d that ChVS m o d i f i c a t i o n changes the parameters and c h a r a c t e r i s t i c s

of HS. The e x p e r i m e n t a l

show that efficient p h o t o s e n s i t i v e h e t e r o s t r u c t u r e s

results

b a s e d on

crystalline

Si and m o d i f i e d ChVS may be obtained.

possibility

to obtain desired parameters and c h a r a c t e r i s t i c s of

these h e t e r o s t r u c t u r e s

There is a

by changing the m o d i f i e r concentration.

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