Optical and electrical properties of GaMnN films grown
by molecular-beam epitaxy
A. Y. Polyakov, A. V. Govorkov, N. B. Smirnov, and N. Y. Pashkova
Institute of Rare Metals, B. Tolmachevsky 5, Moscow, 109017, Russia
G. T. Thaler, M. E. Overberg, R. Frazier, C. R. Abernathy, and S. J. Pearton
a)
Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611
Jihyun Kim and F. Ren
Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611
͑Received 20 May 2002; accepted 30 July 2002͒
Optical absorption spectra, microcathodoluminescence ͑MCL͒ spectra, and electrical properties of
GaMnN films grown by molecular-beam epitaxy with Mn concentration in the range of 3 to 10 at. %
were studied. Optical absorption and MCL spectra show the presence of strong bands corresponding
to the transition from the Mn acceptors near E
c
Ϫ2 eV to the conduction band. The other strong
band observed in MCL measurements was the blue band peaked near 2.9 eV and associated with the
transition from the valence band to deep donors with a level near E
c
Ϫ0.5 eV. All GaMnN samples
were shown to be lightly n-type which suggests close self-compensation of the Mn acceptors by
some native defect donors. A plausible scenario is that such compensating donors could be due to
nitrogen vacancies and that the E
c
Ϫ0.5 eV donor defects are complexes between the Mn acceptors
and the nitrogen vacancy donors. © 2002 American Institute of Physics.
͓DOI: 10.1063/1.1510597͔
I. INTRODUCTION
The doping of GaN with Mn has been of great interest
recently because it was predicted that GaMnN solid solutions
might be magnetic semiconductors with a Curie temperature
higher than room temperature.
1,2
Recently, it was indeed
shown that GaN films doped with Mn either by diffusion, ion
implantation, or in the process of growth by molecular-beam
epitaxy ͑MBE͒ show Curie temperatures close to or even
above room temperature.
3–6
Successful growth of GaMnN
solid solutions by metalorganic chemical vapor deposition
͑MOCVD͒ was reported although the magnetic properties of
such samples were not studied in detail.
7,8
However, these
GaMnN films were used to obtain important information on
the position of levels introduced by Mn into GaN. It was
shown that the Mn forms a deep acceptor level near E
v
ϩ1.4 eV
7
and optical absorption and photoluminescence
bands corresponding to transitions from this level to both
bands were detected. It would be very interesting to perform
similar studies on GaMnN films grown by MBE and have
well established magnetic properties. This was the principal
aim of the present article.
II. EXPERIMENT
GaMnN films studied in this article were grown by MBE
on sapphire substrates as discussed in detail previously.
4,9
The Mn concentration was measured by Auger spectroscopy
and also from magnetic susceptibility measurements. The
thickness of all layers was near 0.4–0.5
m and they were
grown using thin low-temperature GaN buffers. The majority
of the films studied in this article were grown at 700 °C, but
some films were also grown at a higher temperature of
750°C. The Mn concentration in the samples ranged from 3
to 10 at. %. The results of the magnetic properties measure-
ments were already published in Refs. 4 and 9. In short,
these measurements showed that the highest magnetization
signal was achieved for a Mn concentration of 3%, with the
Curie temperature going down for higher Mn concentrations
because of the onset of Mn–Mn antiferromagnetic
interactions.
1,2
X-ray analysis and transmission electron mi-
croscopy ͑TEM͒ studies showed that MBE-grown GaMnN
samples were single phase up to the Mn concentration of
about 8% at our particular growth temperatures.
In the present study, a set consisting of an undoped-GaN
film, three GaMnN films with the Mn concentration of 3%,
5%, and 10% and a GaMnN film with Mn concentration of
3.5% was studied. All films but the 3.5% sample were grown
at 700 °C. The 3.5% sample was grown at 750°C. On these
samples, we measured the room-temperature optical trans-
mission using a Hitachi 330 UV-visible spectrophotometer,
microcathodoluminescence ͑MCL͒ spectra at 90 K and 300
K, the electrical resistivity and mobility at room temperature,
and the temperature dependence of resistivity by the van der
Pauw method. We also carried out capacitance–voltage
(C–V) measurements at frequencies from 10 Hz to 10 MHz
at temperatures up to 400 K using Au Schottky diodes pre-
pared by vacuum evaporation through a shadow mask. A
more detailed description of the MCL measurements can be
found, e.g., in Refs. 10 and 11. Other measurements were
fairly standard.
a͒
Electronic mail: spear@mse.ufl.edu
JOURNAL OF APPLIED PHYSICS VOLUME 92, NUMBER 9 1 NOVEMBER 2002
49890021-8979/2002/92(9)/4989/5/$19.00 © 2002 American Institute of Physics