III-V Nitride Growth Studies by Metalorganic Chemical Vapor Deposition
(MOCVD)
Our group has sought in the area of III-V nitrides the possibility of exploring
new generations of semiconductor devices suitable for high-temperature/high-power
electronic and optical, i.e. blue light LED and UV detector applications. In preparing
the ground for these developments we focused on fundamental growth studies of III-V
Nitrides, keeping as a prime objective to understand the growth of these materials and
propose systematic growth approaches rather than entirely empirically based growth
optimizations.
Our research program includes experimental, but also theoretical, studies of
growth. A unique feature which resulted from the studies is the possibility of cubic GaN
growth rather than hexagonal material, which has traditionally been grown up to now. The
results obtained in these studies are summarized below:
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Demonstration of the growth feasibility of GaN and AlN at low temperatures
using a new precursor (phenylhydrazine) for nitrogen. Growth took place in the mass
transport limited regime, which was from 470C to 600C.
-
Evaluation of phenylhydrazine-grown GaN films by XPS and confirmation of
simultaneous presence of both atomic N and partially dissociated fragments of
NH and NH2. Both Ga-N and Ga-O bonds were detected, resulting in a shift of the
Ga3d peak to higher binding energy.
-
Demonstration of cubic GaN with lattice constant of 4.52 A on (100)
GaAs using NH3. A critical temperature window from 600C to
650C was found to be necessary for growth of cubic material, while hexagonal structures
were found above and below this range. Growth rates were ~0.63 um/hr.
-
Development of a theoretical Monte-Carlo based formalism for the
investigation of GaN growth mechanisms.
-
Evaluation of the impact of growth parameters on the growth rate and quality of the growth
of GaN using a Monte-Carlo simulator developed as part of a collaborative effort on
nitrides with Professor J. Singh in our university. The results indicated the following
trends, which provide better insight into the growth mechanisms:
-
At a given temperature and V/III ratio, the lower the Ga flux, the better the
quality of the growth front.
-
At a given growth rate there is a temperature window within which a high
quality growth front can be obtained.
-
For a given growth temperature, the lower the V/III ratio, the better the growth front.
-
Demonstration of strong dependence of cubic GaN/XRD linewidth on growth
temperature and need of low nitridation temperatures for better quality cubic GaN on (100)
GaAs.
-
Demonstration of photoluminescence characteristics down to 77K from GaN
grown on (100) GaAs and analysis of the PL features as a function of temperature and
excitation energy.
-
Assignment of band-edge photoluminescence near 3.36eV and 3.15-3.31eV in
apparently cubic GaN to intrinsic/bound excitons and phonon-assisted, donor-acceptor pair
recombination respectively.
-
Deduction of a free exciton energy of 3.375eV from photoluminescence
measurements at 6.5K of GaN grown on (100) GaAs.
-
Demonstration of Raman scattering from GaN grown on (100) GaAs by
evaluation of strong peaks at 560 cm^-1 and 736cm^-1, corresponding
to TO and LO phonon modes of cubic material.
-
Evaluation of a strong polarization dependent Raman peak from GaN on (100)
GaAs associated with the LO phonon at 736cm^-1. The same oscillating
behavior observed from LO-GaAs and LO-GaN intensity suggested some
in-plane orientation for GaN and GaAs growth and confirmed the coherent GaN
growth.
-
Demonstration of cubic GaN growth on (111) GaAs substrates with a
diffraction peak
at 2 TETA =34.4 degree and a minimum FWHM of 12 minutes.
-
Verification of (111) fcc growth on (111) GaAs by four-circle x-ray
diffractometry and distinction of this structure from (1011) material by
stacking sequence verification.
-
Demonstration of narrower FWHM in XRD peaks of GaN grown on (111)A
rather than (111)B face of GaAs.
-
Demonstration of photoluminescence and Raman scattering characteristics
from GaN on (111) GaAs with similar features as GaN grown on (100) GaAs.
-
Demonstration of a well-defined interface without the presence of oxide or other
interface layers by High-Resolution TEM of GaN grown on (111)A GaAs.
[GaN]
[InP]
[GaAs]
[MOCVD]
[Mixer]
[Gunn (NDR)]
[PIN]
[HBTs]
[HEMTs]
[MMICs]
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Solid State Electronics Laboratory,
Department of Electrical Engineering and Computer Science,
University of Michigan
The homepages are maintained by Xin Zhu