The non-polar m-plane GaN film and polarized InGaN/GaN light-emitting diode (LED) grown by metal-organic
chemical vapor deposition (MOCVD) on LiAlO<sub>2</sub>(100) substrates were investigated. Firstly, the simulation of excitonic
transition energies and polarization effects on band structure of non-polar plane GaN was studied using the k· p
Hamiltonian approach. Due to small lattice mismatch between GaN and LiAlO<sub>2</sub> substrate, X-ray diffraction (XRD)
revealed that the obtained m-plane GaN film has only [11-00] orientation with single-crystalline quality. In addition,
anisotropic crystallographic properties and strain were found, which originates from the broken hexagonal symmetry.
The anisotropic strain further separates the energy levels of top valence band at Γ point. The energy splitting as 37meV
as well as in-plane polarization anisotropy for transitions are found by the polarized photoluminescence spectra at room
temperature, which is consistent with our simulation. The fabricated InGaN/GaN LED on LiAlO<sub>2</sub>(100) emits green
polarized light at room temperature. And the polarization degree of the emission reaches up to 60% at the wavelength of
Ge films have been deposited on Si (100) substrates with graded Si<sub>1-x</sub>Ge<sub>x</sub>:C buffers by chemical vapor deposition (CVD)
method. Based on the Auger electron spectroscopy result, a growth model for the buffers has been proposed, in which
the buffers are thought to be composed of two layers. One is the Si<sub>1-x</sub>Ge<sub>x</sub>:C epilayer due to the reaction of GeH<sub>4</sub>, C<sub>2</sub>H<sub>4</sub>
and Si atoms diffusing up from the substrate, and the other is the Si<sub>1-x</sub>Ge<sub>x</sub> layer due to the reaction of Si and Ge atoms
diffusing down from the Si<sub>1-x</sub>Ge<sub>x</sub>:C epilayer. The energy dispersive spectroscopy result indicates that Ge atoms diffuse
further when the growth temperature is higher, demonstrating the growth model indirectly. With the graded buffers,
epitaxial Ge films show the perfect crystalline quality, and the excellent transport property with the electron mobility
approaching that of bulk Ge materials at the same doping level.
In this paper, the defects in hexagonal GaN epitaxial layers grown on (0001) sapphire (Al<sub>2</sub>O<sub>3</sub>) substrates by HVPE with a
horizontal tube reactor had been studied. The GaN epitaxial layers were etched by means of defect-selective etching
(Orthodox etching in molten KOH). The samples were characterized by Scanning Electron Microscopy (SEM) and
Cathodoluminescence spectra (CL). From surface morphology and cross-sectional images, the defects could be divided
into various types: cracks, low angle grain boundary (LAGB), nano-pipes and dislocations. These different defects were
discussed. The cracks were proposed as related to the strain. And the strain could not only come from the lattice
mismatch and thermal mismatch between sapphire and GaN layer in their interface, but also from the HVPE growth
process. It was found that these screw, mixed and edge type dislocations formed small hexagonal pits after etching.
Some pits would be observed in the area near LAGB. Additionally, by CL mapping technique, some non-radiative
recombination centers without surface terminations could be probed optically.