We demonstrate that GaN can selectively grow by metalorganic chemical vapor deposition into the pores and laterally over the nanoscale patterned SiO2 mask on a template of GaN∕AlN∕Si. The nanoporous SiO2 on GaN surface with pore diameter of approximately 65 nm and pore spacing of 110 nm was created by inductively coupled plasma etching using anodic aluminum oxide template as a mask. Cross-section transmission electron microscopy shows that the threading-dislocation density was largely reduced in this nanoepitaxial lateral overgrowth region. Dislocations parallel to the interface are the dominant type of dislocations in the overgrown layer of GaN. A large number of the threading dislocations were filtered by the nanoscale mask, which leads to the dramatic reduction of the threading dislocations during the growth within the nano-openings. More importantly, due to the nanoscale size of the mask area, the very fast coalescence and subsequent lateral overgrowth of GaN force the threading dislocations to bend to the basal plane within the first 50 nm of the film thickness. The structure of overgrown GaN is a truncated hexagonal pyramid which is covered with six {11¯01} side facets and (0001) top surface depending on the growth conditions.

In this study, the effects of periodic Si delta-doping on the morphological and optical properties of GaN films grown on Si (111) substrate have been investigated. It is found that the flow rate of Si dopant during growth significantly affects the surface morphology, structural and optical quality of GaN. Compared to undoped GaN on Si(111), films grown using periodic delta-doping show a significant reduction of the in plane tensile stress, which is confirmed by the blueshift of the E2(TO) phonon and band edge photoluminescence peaks. The crack density in GaN films also reduces due to delta-doping.

The morphological evolution of AlN buffer layers grown on (111) silicon at high-temperature has been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The structure and morphology of subsequently grown GaN films were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) measurements. It was found that even though thicker AlN buffer layers are the poor single crystal with some defects like mis-oriented domains, stacking faults, they provide better templates for subsequent growth of GaN films with better crystalline and optical properties, compared to the GaN grown on a thin AlN buffer layer. To prevent the formation of SiN x layers at the interface, TMA was flowed for several seconds prior to the introduction of ammonia into the chamber. The AFM result showed that quasi 2-dimensional growth was quickly achieved for the AlN buffer layer with TMA pre-treatment.

In this study, micro-Raman spectroscopy has been used to investigate the vibrational properties of laterally epitaxial overgrown ͑LEO͒ GaN. The LEO GaN films were grown by metal organic chemical vapor deposition on a 2 in. sapphire substrate with SiN mask. Photoluminescence and polarized Raman scattering measurements have been performed in the two regions of GaN growth ͑wing and window regions͒. Raman scattering results are consistent with the lateral growth of GaN in the overgrown region. We have observed second-order Raman scattering in the wing and window regions of GaN. The observations of longitudinal optical phonon plasmon modes in the overgrown region demonstrate that LEO GaN is doped. We have carried out micro-Raman mapping of the local strain and free carrier concentration in the LEO GaN. Anharmonicity due to temperature in LEO GaN has also been investigated. The anharmonicity was found to increase with increasing temperature, and such temperature-induced anharmonicity introduces changes in the linewidth and line center position of the Raman active phonons. The phonon lifetimes in GaN are estimated in the LEO region as well as in the coherently grown region ͑window region͒.