Interband Optical Properties of the Microcrystalline Component within the Damage Layer of Be + - Implanted GaAs
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INTERBAND OPTICAL PROPERTIES OF THE MICROCRYSTALLINE COMPONENT WITHIN THE DAMAGE LAYER OF Be -IMPLANTED GaAs G.F. FENG
AND R. ZALLEN
Department of Physics, Virginia Tech, Blacksburg, VA
24061
USA
ABSTRACT layer in unannealed Be+-implanted GaAs samples (45-keY Be+
damage
The
ions, 1013 to 5 x 1014
ions/cm 2)
consists
of
a
fine-grain
mixture
of
amorphous GaAs and GaAs microcrystals, with the characteristic microcrystal size
L
of
fluence.
the
microcrystalline
component
decreasing
We have carried out reflectivity measurements
with on
increasing
these
samples
for photon energies from 2.0 to 5.6 eV, in the electronic interband regime. Using
Lorentz
oscillator analysis and the effective medium approximation,
we have extracted the dielectric function of the microcrystalline component (p-GaAs) within the damage layer.
The optical properties of p-GaAs deviate
appreciably from those of the bulk crystal near
the
peaks.
found to increase over the
The
linevidths
of
these
peaks
are
bulk-crystal value by an amount proportional to (l/L), about
eV when L - 100 A.
0.2
interband the
absorption
increase
being
These finite-size effects can be understood
in terms of a lifetime reduction caused by the
short
time
it
takes
for
electrons to reach the microcrystal boundaries.
INTRODUCTION In a recent study of near-surface damage GaAs,
Holtz et al.
in
unannealed
Be -implanted
[1] used a combination of Raman scattering and chemical
etch to obtain microstructural information for samples subjected to various fluences. fraction
Information f
,
the
derived
characteristic
dependence.
Here
we
report
reflectivity
experiments
on
the the
included
the
microcrystal results same
of
microcrystalline size
L,
visible
volume
and their depth and
ultraviolet
Raman-characterized samples.
One
purpose of this work is to determine the effect of microcrystal size in the 100-A
range
on
microcrystalline
the GaAs
optical
properties
(p-GaAs).
been extensively investigated [2],
While
and
interband
excitations
little is known about p-GaAs.
Mat. Res. Soc. Symp. Proc. Vol. 128. t1989 Materials Research Society
in
microcrystalline Si has recently
672
EXPERIMENT The
samples
(100)-oriented wafers which had been implanted with
were
No post-implant anneal was
45-keV Be+ ions incident at 9* from the normal. done.
Further
details
of
are
preparation
sample
given
in
Ref. 1.
Reflectivity measurements were performed with a prism-grating spectrometer, using
chopped
and
radiation
lock-in
a
in the following sections, will be given in preparation on this work (3]. 1
Figure
shows
of
Details
detection.
the
as well as of the analysis techniques mentioned
calibration,
reflectivity
more
complete
article
in
our results for the reflectivity spectra R(E) of four
Panels (a), (b), (c), and (d) show the 13 13 spectra observed after implantation with fluences of 1 x 10 , 5 x 10 2 14 14 ions/cm , respectively. Along with the data on the 1 x 10 , and 5 x 10 in
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