Lawrence Berkeley National Laboratory
Recent Work
Title
DIRECT MEASUREMENT OF GAP STATE ABSORPTION IN HYDROGENATED AMORPHOUS
SILICON BY PHOTOTHERMAL DEFLECTION SPECTROSCOPY
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https://escholarship.org/uc/item/5hg8s219
Authors
Jackson, W.B.
Amer, N.M.
Publication Date
1981-08-01
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IT[1
Lawrence
Berkeley
Laboratory
Ii:I
UNIVERSITY
OF
CALIFORNIA
ENERGY &
ENVIRONMENT
DIVISION
Submitted
to
Physical
Review
Letters
DIRECT
MEASUREMENT OF GAP
STATE
ABSORPTION
R £
~!E~
£ D
IN
HYDROGENATED AMORPHOUS
SILICON
BY
llE~ELEYLA8ORATO~
PHOTOTHERMAL
DEFLECTION
SPECTROSCOPY
.
fEB
1
1982
Warren
B.
Jackson
and
Nabi1
M.
Amer
August
1981
UiJRARYANO
DOCUMENTS SECTION
TWO-WEEK
LOAN
COpy
Prepared for the U.S. Department of Energy under Contract W-7405-ENG-48
DISCLAIMER
This document was prepared
as
an account
of
work sponsored by the United States
Government. While this document is believed to contain correct information, neither the
United States Government nor any agency thereof, nor the Regents
of
the University
of
California, nor any
of
their employees, makes any warranty, express or implied, or
assumes any legal responsibility for the accuracy, completeness, or usefulness
of
any
information, apparatus, product, or process disclosed, or represents that its use would not
infringe privately owned rights. Reference herein to any specific commercial product,
process, or service by its trade name, trademark, manufacturer, or otherwise, does not
necessarily constitute
or imply its endorsement, recommendation, or favoring
by
the
United States Government or any agency thereof, or the Regents
of
the University
of
California. The views and opinions
of
authors expressed herein do not necessarily state or
reflect those
of
the United States Government or any agency thereof or the Regents
of
the
University
of
California.
l
-
-_J
\,,1
o
DIRECT
MEASUREMENT
OF
GAP
STATE
ABSORPTION
IN
HYDROGENATED
AMORPHOUS
SILICON
BY
PHOTOTHERMAL
DEFLECTION
SPECTROSCOPY
Warren
B.
Jackson
and
Nabil
M.
Amer
Applied
Physics
and
Laser
Spectroscopy
Group
Lawrence
Berkeley
Laboratory
University
of
California
Berkeley,
California
94720
This
work was
supported
by
the
Assistant
Secretary
for
Conservation
and
Solar
Energy,
Photovoltaic
Systems
Division
of
the
U.S.
Depart-
ment
of
Energy
under
Contract
No. W-7405-ENG-48.
DIRECT
MEASUREMENT
OF
GAP
STATE
ABSORPTION
IN
HYDROGENATED
AMORPHOUS
SILICON
BY
PHOTOTHERMAL
DEFLECTION
SPECTROSCOPY
..
ABSTRACT
We
have
used
the
highly
sensitive
technique
of
phototh-
ermal
deflection
spectroscopy
to
directly
measure
the
sub-
gap
optical
absorption
of
undoped,
singly
doped,
and
compen-
sated
a-Si:H
down
to
0.6
eVe
We
show
that
the
gap
state
absorption
is
due
to
dangling
silicon
bonds.
We
also
present
evidence
that
while
doping
creates
defects,
compen-
sation
removes
them.
PACS:78.50.Ge,78.65.Jd,78.40.Fy,07.65.Eh
In
amorphous
semiconductors,
the
optical
absorption
of
defects
and
impurities
is
most
readily
observed
below
the
band
edge
since
it
is
not
obscured
by
the
much
larger
band-to-band
absorption.
Consequently,
sub-gap
absorption
spectra
should
provide
information
about
defects
in
amorphous
materials.
Although
such
measurements
have
been
made
on
chal-
cogenide
1
glasses,
none
of
the
measurements
made
on
hydrogenated
amor-
phous
silicon
(a-Si:H)
have·
been
reliable
because
of
experimental
limi-
tations.
The
films
are
typically
1
~m
thick
and
are
not
optically
homo-
geneous,
making
conventional
transmission
and
reflection
measurements
of
absorption
coefficients
-1
2
(
a)
below
50-100
cm
unreliable.
Derivation
of
the
absorption
from
photoconductivity3,4
requires
reliance
upon
the
experimentally
unverified
assumption
that
the
n~T
product
is
independent