Improved Stability of RF Glow Discharge Deposited a-Si:H Achieved by Hydrogen Dilution of Silane.
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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
