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IHPROVED STABILITY OF RF GLOM DISCHARGE DEPOSITED a-Si:H ACHZEVEO BY HYDROGEN DILUTION. OF GILANE.

R.C.

van Dart,

Delft

H.J.

University

Hekelweg 4,

Geerts, of

d.C.

van den Heuvel,

Technology,

NL-2628 CD Delft,

Faculty

of

Electrical Engtnearin8,

the Netherlands.

ABSTRACT.

The

magnitude

of

metastable

light-Induced

degradation

of intrinsic

hydrogenated amorphous silicon films deposited by rY glow discharge from different

selene-hydrogen

mixtures

wan

studied.

By

stone of space-

charge-limited current measurements the Fermi-lava1 density of states was determined for as-grown and light-soaked n+-t-n+ devices. Films deposited using a mixture of 55 vol.S stlane and 45 vol.S hydrogen and a relatively high rf power level of 62 n•J/cm2 to obtain a high growth rate exhibited an improved stability with regard to light-Induced degradation of

the

pure

film,

etlane

and

conditions in

compared an

with films grown under Lha conditions of using

rf

power Just sufficient to seintaln the plasma,

known to ylald good quality films. The results are explained

terms of an improvement in

the structural oraer of the film.

INTRODUCTION.

Hydrogenated material

for

transistors.

amorphous

electronic Light

silicon

devices

exposure

(a-St:H)

such

results

as in

has become an important

solar

cells and thin film

metestable

changes

in

the

material, significantly influencing the performance of a-St:H solar cells. The efficiency Is reduced. Annealing at 180 °C for about half an hour

restores

Mronekt

conductivity, and

the original slate.

effect

(SUE) the

[1].

spin

There

the dangling bond,

The deposition substrata

most from

common

and it

is

at

the dark- and photo-

and

least

sub-gap absorption

one type of light-Induced

Is located near mtdgep.

deposition

stlane.

temperature

known as the Staebler-

density as measured by ESR,

photolusinaacense.

defect,

The affect i8

Changes are observed in

method

ls

the

rf-glow-discharge

The influence of parameters such as rf power, stlane dilution with inert noble Basses hoe

Mat. Res. Sac. Syrup. Proc. Vol. 118. • 1988 Materials Research Society

174

well

been

described.

quality, films. just

of

rf

lead

that it

6

with

growth

The

Recently we have

possible to improve the

rate

of the films was

36 nm/mmn.

for films deposited under standard conditions

nm/min.

conditions

deposition

dilution

is

by using a silane-hydrogen mixture and a relatively

level.

to

The

to conditions resulting in good

maintain the plasma are used [2].

a-Si:H

power

compared [3].

has

conditions pure silane and an rf power level

by means of PDS-measurements,

quality high

This

these

to

sufficient

proven,

(rf

level,

power

degree

of silane

been systematically changed in order to

have

hydrogen)

the influence of these parameters on the midgap density of states

study of

In

as-grown

intrinsic rf-glow-discharge deposited a-

light-soaked

and

Si:H.

EXPERIMENTAL SETUP.

The deposition apparatus used was an rf glow discha