ISSN 10637834, Physics of the Solid State, 2010, Vol. 52, No. 9, pp. 1850–1854. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © I.G. Aksyanov, M.E. Kompan, I.V. Kul’kova, 2010, published in Fizika Tverdogo Tela, 2010, Vol. 52, No. 9, pp. 1724–1728.
1850
1. INTRODUCTION
Silicon carbide is a widebandgap semiconductor
material that exhibits a number of valuable properties.
In particular, devices based on silicon carbide can
operate at higher temperatures and powers as com
pared to devices based on silicon [1]. In recent years,
there has appeared one more direction in the use of
this material. Silicon carbide (SiC) thin films have
been used as intermediate layers in the growth of films
of hexagonal semiconductors
A
3
B
5
on silicon sub
strates. In this case, stresses induced by the lattice mis
match between the
A
3
B
5
film and the substrate are
concentrated in the transition layer. Compared to alu
minum nitride AlN, which has also been used for these
purposes, silicon carbide has additional advantages.
Depending on the growth conditions, this material
can form a complex heterogeneous structure consist
ing of regions of different polytypes and, as a result,
can be adjusted to local atomic configurations, thus
decreasing distortions in grown films.
Earlier studies on electron diffraction [2] and lumi
nescence [3] revealed that regions of different poly
types coexist in the films under investigation. This
work is devoted to investigation of the composition of
mosaic thin films of silicon carbide by Raman spec
troscopy. We also discuss how the mosaic structure of
films can affect the Raman spectra.
Light scattering from lattice vibrations in single
crystals of different polytypes of silicon carbide was
previously investigated in detail by different authors
(see, e.g., [4, 5]). The data obtained in these works
provide the basis for the analysis of the Raman scatter
ing spectra measured in our work.
As is known, different crystal modifications of sili
con carbide are very close in values of many parame
ters. They are formed from identical layers of silicon
and carbon that are arranged in a somewhat different
order. For this reason, the phonon dispersion curves
for SiC of different crystalline modifications differ
insignificantly, which complicates the separation of
lines corresponding to individual polytypes.
However, the Raman scattering in silicon carbide
exhibits an interesting feature. In view of the presence
of multiple periods in the crystal lattice (e.g., 6layer
period for the 6
H
polytype, 15layer period for the 15
R
polytype, etc.), the material with long periods in the
crystal lattice has shortened bands in the
k
space. They
are usually represented as fractional parts of a large
phonon band in the
k
space (folded zone) [4]. As a
result, the boundaries of minibands in the
k
space
superimpose on the region
k
= 0. At these points of the
dispersion curve, the light scattering becomes allowed
by the selection rules.
In particular, this makes it possible to record lines
of acoustic vibrations in the backscattering geometry.
Since the large zone for each polytype is divided into a
relatively small integral number of minibands (its own
in each case), the miniband boundaries are located at
different welldefined points of the spectrum, even
though the initial dispersion law for the large zone dif
fers insignificantly for different polytypes.
In our case, the investigation of the Raman spectra
of mosaic thin films in the range of acoustic vibrations
allowed us to reveal additional small inclusions of
polytypes that do not manifest themselves in the fre
quency range of optical vibrations.
2. SAMPLE PREPARATION
AND EXPERIMENTAL TECHNIQUE
We investigated silicon carbide films grown by
solidstate epitaxy on singlecrystal silicon substrates
with the {111} orientation [6, 7]. The film thickness
was of the order of 200 nm. The luminescence of the
films was investigated in our earlier work [3].
SEMICONDUCTORS
AND DIELECTRICS
Raman Scattering in Mosaic Silicon Carbide Films
I. G. Aksyanov, M. E. Kompan*, and I. V. Kul’kova
Ioffe PhysicalTechnical Institute, Russian Academy of Sciences,
Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia
* email: kompan@mail.ioffe.ru
Received December 22, 2009
Abstract
—The Raman spectra of mosaic silicon carbide films grown on silicon substrates by solidstate epi
taxy have been studied. The main polytypes forming the film material have been determined. It has been
experimentally revealed that the properties of the silicon carbide film are changed after an aluminum nitride
film is deposited on the former film. This has been interpreted as a manifestation of good damping properties
of the SiC film when layers of other semiconductors are grown on it.
DOI:
10.1134/S1063783410090106