a-Si:H interface

Journal of Non-Crystalline Norlb-l~olland,Amsterdam

VOLTAGE

Solids 90(1987)343

343

DEPENDENT

OF THE 01/r-Si:H

Peng

Chen

INTERNRL

PHOTOEMISSION

STUDY

OF THE

ENERGY

BRND

Su

Zinin

and

Lin

Zainin

of

Physics,

Zhongshan

of

Physics,

Lanzhou

University,

Gurngzhou,

China

Guanghua

Department

University,

Lanzhou,

China

The voltage dependence of photoemission current in an structure has been investigated. From the I-V characteristic, energy band structure near the Alla-Si:H interface are determined. band bending of 0.20 ev is found at the Alla-Si:H interface.

I.

Al/a-Si:H/c-Si details of the An upward

INTRODUCTION The

energy

current

band

transport

has

to

investigate

2.

PRINCIPLE The

of

voltage

widely

used

in

band

studied

photon

energy

height,

the

electronic

and

the

in

of

be

writen

where

ELXo) q is

Projects

0022-3093/87/$03.50 (North-Holland

the

Physics

or

and

current 3

Powell

,

the

still

injecting the

the

purely

attempt

of

current,

HIS

devicesle3,

holes

(positively

relating

to

interface depends

upon

interface.

magnitude

of

the

barrier the

According the

photoemssion

as - *

+

charge;

by

OElsevier Publishing

the

1/2E(*o,1/2,p

(q/4%6) ')

= -q/llbn8Xo

electronic

supported

by

of

of

of the

a new

Besides

light

the

for

still

interface.

a-Si:H.

photoemission

is

photoemission

biased)

into

near

and here

properties

incident

layer

proposed

I = A 1 hv and

the

metal the

internal

metal/a-Si:H

(negatively

of

a-Si:H

of

metal

understanding

We report

interface

the

electrons

intensity

the

of

at

from

model

scattering

study

with

the barrier

physics. dependence

occurs

magnitude field

can

of

a-Si:H for

siliconschottky

structure

here

of

important

interface

of

the

interface

very

an amorphous

technique

been

the

is

of

photoemission

biased1

current

it

understanding the

which

near*

since

properties

applying

the

structure

interest,

fundamental

l

STRUCTURE

INTERFKE'

Shaoqi,

Department

-346

Science

= -V/d

+ El(Xo)

8

dielectric

the

Fund

Science Publishers Division)

of

B.V.

the

e-x0/1

(2) constant

Chinese

of

Academy

a-SilH;

of

V

Science.

the

applied

voltage;

layer;

El

the

x0

interface;

injecting carriers;

I

intensity

of

energy metal

-wave

the

constant

the

from

(photon

3 to From

Ill

and

In

injecting

interface I-V

the

the

harrier

(X0

no

integral

<<

by

charge

in

2 to of

eq.Il)

be

added

on

values

of

In

case

the with by

the

emitting

related

depends

33.

a-Si:H and

for

A a constant which

the

aarimun

interface

path;

only

the the

to

the

the

electron

p for

emission

of

continuous

respect

one

equal

to

and

photon

then

maximum -x0/1 term e

effect

in

range

new

field exciting

to

the

approaches

1,

then

barrier current

in

force

therefore,

but is

the

opposite

higher

due

gives

is

potential.

magnitude light

vanishes

injecting

low-field

closed

image

current

the

is

field-dependent

the

surface the

photoemission and

photoemission

of

bias,

field

of the

photoemission

threshold

internal

potential

scattering the

of

regime

the

energy

the

dependence

however,

to

the

the

high-field

scattering by

carrier

not,

This the

and

that

into

regime,

is

or

shown

dominated

whether

effect. of

1 I

free

field matter

is divided

low-field

energy

magnitude

to

than

the

scat-

direction

and

interface.

EXPERIMENTAL The

sample

used

in

diode,

in

which

Al

layer

barrier and

the

light

is

from of

bulk

lamp

In

is

there

no

seperate the

emission value

of the

In

figure

2V

found

2,

be as

the

two used

photoemission

is

of

deposited

Schottky at The

< l.lev For

light of

fundoped) sputtering

200!.

energy

a filter.

types the

by about

carriers

obtained the

be

the

effect

decreased

injecting of

250'~

incident

),

reducing should

substract

from

Schottky

two

diode

it.

measurement the

and

dark

activation

applied

hole

current

at

represents

the to

internal the

of

the

1 shows

230k.

114

a-Si:H

the

A bias

that field

power

measure-

(E,l

Figure

voltage

injection and

conductivity

energy

respectively.

the

upward

Ill/a-Si:H

incident

as

in

of

case

as

the

IE opt 1 and 9 and 0.92ev,

1.80ev

interface the

is

absorption gap

a function

in

(Ll/Si:H

avoid

absorbtion

band

current

at

to

an

is

( photon

slice of

is

thickness

beam

a c-Si

c-Si

optical

to

with

intensity

optical

optical

determined

using

order

that

(d=O.Sum)

infrared

by the

synchronously,

experiment

a-Si:H

semitransparent

trappingq,

From

present the

is

interfaces

ment,

the

a continuous-wave

a tungsten

appropriately.

are

the

regime,

is

the

applied

tering

the

Typical

from

p should

it be

high-field

influenced

sign,

free

range ),

any potential

of

layer.

of

(2), will

the

In

When

(_ hv

from the

p a constant

injecting

values

characteristic

lowering.

in

and

light

energy the

voltage

regime.

greatly

height mean

light; the

of

4.

on

the

barrier

resulted

position

scattering

that

eqs.

current

the

monochromatic

shows

field the

incident in

by

light

energy

electric between

@

distribution

from

3.

the

distance

photo-

threshold

the

band

is

2.5x104V/cn.

versus

the

bending

square

so

root

of

the

linearity

of

p equal

to

barrier

tatol

4.

Ill4

By

heights

1.12ev

and

electric

the

EL'*

the

-2s :

-15 :

:

a

the

electron

injection

in

interface

is

high-field

11'4

"I, and

El'* hole

plotted.

regime

gives

Cut-Yes

to

injection

zero

are

The the

good

value

of

current,

the

determined

to

be

respectively.

“‘-J 600..

IxlO”Wcmz

400..

D

200.. ,

"ear

cur-"es

extrapoldtlng for

0.97ev,

field

vs..

D 00

:,u--l

op

-5

a1 ~ o

Do FIGURE

85

15

25

Vlvolt.

-I-

0 0

0

D

1 current as of applied voltage caeee of electron and hole injection.

Photoemission function for both injection

I

a

-2..

injection.

0.00

0.02

0.04

0.06

0.08

BE”Zle”l

4.

DISCUSSION From

barrier

the

above

diode

IS

(O.ZOev) height

of week

the

values It

of optical

obtained

i5

a5

electron

of

the as by

the be

photoenissla" absorption

width

band

of

bending

mentioned

energy

shou"

band

in

that

neasureeent measurement.

a"

the

space-charge

the

undoped

internal

band

gap

This

a-Si:H

lllla-Si:H of

derived

ie

a rather

commonly

at from

!arqer

is the

the than

strong

Schottky

the

from

(O.lbua)

field

0.29ev ie

the value energy

layer

the

1 is

The

actrvatlon

because

(2.09~

of

3.

the

and

dldqran

figure

subtracting

injection, The

n-type.

should

results, depicted

hand

bending

the

barrier considered

evaluated

from

interface. voltage that evidence

dependence obtained

from that

the

Energy Al/a-Si:H

FIGURE 3 band diagram Schottky

nobility

gap

optical

gap

The

contact

5

of

band the

is

and

bending

obviously

and

present

the

at same

its

different

magnitude

measurement 697 . surface

native-oxide

observed by

a-Si:H

in

magnitude

with

the

Goptl. g

from

bending caused

(Em)

upward

derived

of the barrier.

different

metal

mechanism

which

are

near

similar This

and

be

the

Alla-Si:H

the

results

similarity

contacts should

to

suggests native-oxide

further

interface of that

Crls-Si:H the

surface

band nay

be

explored.

REFERENCES II

Alvin

M.

21

R.J.

Powell,

Goodman,

3)

C.N.

Berglund

4)

Z.H.

Su

51

R.P.

Street,

61

S.Q.

Peng,

7)

B. Aker, S.Q. (19831 509.

and

Phys.

J. and S.Q.

Phys.

R.J.

J.

Peng,

and S.Y.

(1966)

588.

(1970) J.

2424.

Appl.

Phys.

Non-Cryst.

Thompson Cai

144 41

Powell,

Peng,

M.J. S.Y.

Rev.

plppl.

and

N.M.

H.Fritrsche, Cai

42

Solids Johnson, Bull.

and

77&7G

H.

11971)

Phil. &PS

Fritrsche,

28

573.

(19851

555.

Msg. (19831 J.

B 51

(1985)

1.

295. Non-Cryst.

Solids

59160