XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
88
T3: O–7
Structural and optical study of As-Te chalcogenide films
prepared by plasma-enhanced chemical vapor deposition
Leonid Mochalov
1,3
, Aleksey Nezhdanov
1
, Mikhail Kudryashov
1
, Alexandr Logunov
1
,
Dominik Dorosz
2
, Giuseppe Chidichimo
4
, Giovanni De Filpo
4
, and Aleksandr Mashin
1
1
Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia,
e-mail: mochalovleo@gmail.com
2
Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Krakow,
Poland
3
Nizhny Novgorod State Technical University n.a. R.E. Alekseev, Nizhny Novgorod, Russia
4
University of Calabria, P. Bucci-15c, Rende (CS), Italy
First time the method of Plasma-Enhanced Chemical Vapor Deposition (PECVD) was
used for preparation of As-Te chalcogenide films of different chemical and phase
composition [1]. Raman spectra of As-Te thin film samples are shown in Fig. 1a. All the
spectra shown here display three broad bands relating to the vibration of units of structural
net that contain Te–Te (about 160 сm
–1
), As–Te (about 197 сm
–1
) and As–As (about 236
сm
–1
) bonds. It was established previously [2–3] that AsTe and As
2
Te
3
phases can be easily
converted to each other by varying of the preparation conditions: As
2
Te
3
⇄
2As + 3Te.
Fig. 1. Raman spectra of As-Te films with different stoichiometry.
Analysis of the optical properties of As-Te films of different macrocontent was based
on the transmission and reflection spectra. The intense interference and a high degree of
transparency of the samples are observed in the 1000–3000 nm region of the spectra. With
increasing of the arsenic concentration in the films the edge of transparency shifts towards
long-wavelength area. The optical bandgap of As-Te films varies in the range of 0.84–1.31
eV (Fig. 1b).
Keywords: As-Te; PECVD; molecular spectroscopy
Acknowledgment
This work was supported by the Russian Science Foundation grant 16-12-00038.
References
[1] L. Mochalov, A. Nezhdanov, M. Kudryashov, et al., Plasma Chem. Plasma P. (2017),
doi:10.1007/s11090-017-9830-xA.
[2] A. Tverjanovich, K. Rodionov, E. Bychkov, J. Solid State Chem. 190 (2012) 271.
[3] D. C. Kaseman, I. Hung, K. Lee, K. Kovnir, Z. Gan, B. Aitken, S. Sen, J. Phys. Chem. B 119(5)
(2015) 2081.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
89
T3: O–8
Raman spectroscopic characterization of GaN layers grown
by high-temperature vapor phase epitaxy
Christian Röder
1
, Mykhailo Barchuk
2
, Tom Schneider
3
, Gleb Lukin
3
,
David Rafaja
2
, Olf Pätzold
3
, and Jens Kortus
1
1
Institute of Theoretical Physics, TU Bergakademie Freiberg, Leipziger Str. 23, 09599 Freiberg,
Germany, e-mail: christian.roeder@physik.tu-freiberg.de
2
Institute of Materials Science, TU Bergakademie Freiberg, Gustav-Zeuner-Str. 5, 09599 Freiberg,
Germany
3
Institute of Nonferrous Metallurgy and Purest Materials, TU Bergakademie Freiberg, Leipziger Str.
34, 09599 Freiberg, Germany
High-temperature vapor phase epitaxy (HTVPE) [1] is considered as a cost-efficient technology
for fabrication of GaN templates, e.g., as an alternative to metalorganic vapor phase epitaxy
(MOVPE). In this work, GaN layers grown by HTVPE on (0001)-oriented sapphire substrates were
investigated by Raman spectroscopy and high-resolution X-ray diffraction (HRXRD). A thin GaN
nucleation layer was deposited on pre-treated sapphire substrates and recrystallized at 1100°C.
Subsequently, this layer was overgrown by GaN using a two-temperature growth regime. A scheme
of the sample structure is presented in Fig. 1a. The resulting GaN layers exhibit a structural quality
comparable to similar MOVPE layers according to the FWHM of 0004 X-ray reflections, which are
below 300 arcsec.
Confocal Raman measurements were performed in backscattering geometry at room temperature
in order to monitor the residual stress within the GaN layers with a high lateral and spatial resolution.
In Fig. 1b, the Raman shift of the non-polar E2high Raman mode is shown in dependence on the
distance from the sample surface. As compared to the frequency of relaxed GaN bulk material [2]
(dotted horizontal line), the spectral position of this phonon mode is shifted to higher wavenumbers
indicating compressive strain. Due to the lattice misfit between sapphire and GaN, higher strain
values are observed close to the interface to the substrate.
a)
b)
c)
Fig. 1. (a) Scheme of the sample structure. (b) Raman shift of the E2high phonon mode as function of the distance
from the sample surface. The dotted horizontal line marks the frequency of relaxed GaN bulk material. (c) The
reciprocal space map of the 0004 X-ray reflection reveals two distinct maxima associated with differently grown
HTVPE GaN layers (A-C). The intensity is displayed in a logarithmic scale.
HRXRD measurements revealed two distinct maxima in the 0004 reciprocal space map (Fig. 1c).
The corresponding lattice parameters c were converted into the wavenumbers of the E2high Raman
mode (solid horizontal lines in Fig. 1b). The calculated wavenumbers coincide well with the
measured ones, which indicates that the peak splitting is due to the residual stress distribution. The
discrete nature of the peak splitting originates from a bimodal stress distribution.
Keywords: Raman spectroscopy, GaN, X-ray diffraction
Acknowledgment
This work is financially supported by the European Union (European Social Fund) and by the Saxonian
Government (grant no. 100231954) as well as the German Research Foundation (contract PA 1236/3-1).
References
[1] G. Lukin et al. Physica Status Solidi C 11 (2014) 491.
[2] V. Yu. Davydov et al. Physical Review B 58 (1998) 12899.
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