Doctor of Philosophy / Department of Chemical Engineering / James H. Edgar / The sublimation recondensation crystal growth of aluminum nitride, titanium
nitride, and yttrium nitride were explored experimentally and theoretically. Single
crystals of these nitrides are potentially suitable as substrates for AlGaInN epitaxial
layers, which are employed in ultraviolet optoelectronics including UV light-emitting
diodes and laser diodes, and high power high frequency electronic device applications.
A thermodynamic analysis was applied to the sublimation crystal growth of
aluminum nitride to predict impurities transport (oxygen, carbon, and hydrogen) and to
study the aspects of impurities incorporation for different growth conditions. A source
purification procedure was established to minimize the impurity concentration and avoid
degradation of the crystal’s properties. More than 98% of the oxygen, 99.9% of hydrogen
and 90% of carbon originally in the source was removed. The AlN crystal growth process
was explored in two ways: self-seeded growth with spontaneous nucleation directly on
the crucible lid or foil, and seeded growth on SiC and AlN. The oxygen concentration
was 2 ~ 4 x 1018cm-3, as measured by secondary ion mass spectroscopy in the crystals
produced by self-seeded growth. Crystals grown from AlN seeds have visible grain size
expansion. The initial AlN growth on SiC at a low temperature range (1400°C ~1600°C)
was examined to understand the factors controlling nucleation. Crystals were obtained
from c-plane on-axis and off-axis, Si-face and C-face, as well as m-plane SiC seeds. In all
cases, crystal growth was fastest perpendicular to the c-axis.
The growth rate dependence on temperature and pressure was determined for TiN
and YN crystals, and their activation energies were 775.8±29.8kJ/mol and
467.1±21.7kJ/mol respectively. The orientation relationship of TiN (001) || W (001) with
TiN [100] || W [110], a 45o angle between TiN [100] and W [100], was seen for TiN
crystals deposited on both (001) textured tungsten and randomly orientated tungsten. Xray
diffraction confirmed that the YN crystals were rock-salt structure, with a lattice
constant of 4.88Å. Cubic yttria was detected in YN sample from the oxidation upon its
exposed to air for limited time by XRD, while non-cubic yttria was detected in YN
sample for exposures more than one hour by Raman spectra.
| Identifer | oai:union.ndltd.org:KSU/oai:krex.k-state.edu:2097/8625 |
| Date | January 1900 |
| Creators | Du, Li |
| Publisher | Kansas State University |
| Source Sets | K-State Research Exchange |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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