High quality GaN–InGaN heterostructures grown on (111) silicon
substrates
J. W. Yang, C. J. Sun, Q. Chen, M. Z. Anwar, and M. Asif Khan
APA Optics Inc., 2950 N.E. 84th Lane, Blaine, Minnesota 55449
S. A. Nikishin, G. A. Seryogin, A. V. Osinsky, L. Chernyak, and H. Temkin
a)
Electrical Engineering Department, Colorado State University, Ft. Collins, Colorado 80523
Chimin Hu and S. Mahajan
Department of Materials Science and Engineering, Carnegie Mellon University,
Pittsburgh, Pennsylvania 15213
Received 30 July 1996; accepted for publication 24 September 1996
We report on the low pressure metal organic chemical vapor deposition of single crystal, wurtzitic
layers of GaN and GaN/InGaN heterostructures on 111 GaAs/Si composite substrates. The
structural, optical, and electrical properties of the epitaxial layers are evaluated using x-ray
diffraction, transmission electron microscopy, photoluminescence, and measurements of minority
carrier diffusion length. These measurements demonstrate high quality of GaN grown on the
composite substrate. © 1996 American Institute of Physics. S0003-69519601849-9
Growth of device quality GaN based heterostructures on
GaAs or Si would be useful for the preparation of high-
temperature, large-band gap devices and their integration
with advanced GaAs or Si technologies. Deposition of zinc
blende GaN layers on Si and GaAs substrates has been re-
ported recently by a number of research groups.
1–7
Both mo-
lecular beam epitaxy MBE and metalorganic chemical va-
por deposition MOCVD were used in these experiments.
The growth of GaN on GaAs generally involves NH
3
induced nitridation of the GaAs surface, followed by the low
temperature 500–600 °C growth of a thin 20–50 nm
buffer layer, and the subsequent growth of the desired epi-
taxial layer. The latter is grown at a high temperature of
750–900 °C in order to assure high optical and electrical
quality. It is well established that in MOCVD growth of the
wurtzite GaN layers on GaAs, photoluminescence efficiency
improves with increasing growth temperature.
6
However,
growth of GaN at temperatures in excess of 800 °C results in
rapid dissociation of GaAs and a significant degradation in
the morphology of the GaN film. The optical quality of such
films is also degraded by the incorporation of As.
6
The use of
silicon substrates can obviate the decomposition problem.
Most of the past experiments on the growth on GaN on
Si focused on the zinc blende structure, i.e., low temperature
growth on 001 Si.
4,5
Relatively little work has been re-
ported on the high temperature growth of wurtzite structure
GaN or AlN on 111 oriented Si
8
and not much is known
about either structural or optical properties of such layers.
In this work, we report a unique dual-growth procedure
for obtaining high quality layers of GaN and GaN/InGaN
heterostructures on 111 silicon substrates. Epitaxial single
crystal structures resulting from our procedure, relying on a
GaAs/Si nucleation layer, show room temperature photolu-
minescence efficiency and minority carrier diffusion lengths
which are comparable to similar structures prepared on basal
plane sapphire. In this letter we describe the details of ex-
perimental procedures and the structural, optical, and electri-
cal characteristics of the epitaxial layers.
Since the 0001 plan of the wurtzitic structure is parallel
to the 111 plane of the diamond cubic lattice we have cho-
sen 111 silicon substrates for our study. The 111 Si sub-
strates used here were cleaned using a two step chemical etch
process. A layer of SiO
2
, which we estimate to be 2 nm
thick, is formed first in nitric acid and then removed in a
dilute HF:water solution.
9
The substrate is then etched in
H
2
O:HCl:H
2
O
2
1:3:1 solution to form a thin, 0.3–0.5 nm,
oxide layer which is then removed in HF:methanol. This
results in a H-passivated surface.
9
When placed in the MBE
chamber, a 11 surface reconstruction can be observed at
room temperature. Heating the sample to 600 °C produces a
clean, oxide-free surface, as measured by reflection high and
low energy electron diffraction RHEED and LEED and
Auger electron spectroscopy AES. The initial layer of
GaAs, 15 nm thick, is grown at 300 °C and the final high
quality layer, 10–20 nm thick, is grown at 550 °C.
9
The GaAs/Si composite substrates were then used to de-
posit GaN single films and GaN/In
x
Ga
1 -x
N heterojunctions
using low pressure metalorganic chemical vapor deposition
LP-MOCVD. The LP-MOCVD growth is initiated by ni-
triding the GaAs layer. This is followed by the deposition of
a thin 20 nm buffer layer of AlN at 600 °C and the growth
of the epitaxial layer of GaN at 900 °C and 76 Torr. This
growth procedure, aside from the higher growth tempera-
tures, is nearly identical to the one used previously for the
growth of GaN films on GaAs substrates.
6
Layers of
In
x
Ga
1 -x
N, with x up to 0.14 and approximately 0.1 m
thick, were deposited at 750 °C using trimethylindium as the
In source.
The macroscopic structure of our layers was studied us-
ing x-ray diffraction. A glancing angle –2 x-ray diffrac-
tion XRD scan taken on a 1-m-thick film of GaN grown
on a GaAs/111Si composite substrate is illustrated in Fig.
1. Only the 0002, at 2=34.6°, and 0004 peaks of -GaN
are observable and there are no detectable contributions of a
a
Electronic mail: htemkin@coe2.coe.ttu.edu
3566 Appl. Phys. Lett. 69 (23), 2 December 1996 0003-6951/96/69(23)/3566/3/$10.00 © 1996 American Institute of Physics