The authors report on pulsed lateral epitaxial overgrowth of aluminum nitride films on basal plane sapphire substrates. This approach, at temperatures in excess of 1150°C, enhanced the adatom migration, thereby significantly increasing the lateral growth rates. This enabled a full coalescence in wing regions as wide as 4–10μm. Atomic force microscopy and cross-section transmission electron microscopy were used to establish the reduction of threading dislocations in the lateral growth. Cross-sectional monochromatic cathodoluminescence and photoluminescence measurements confirmed the improved optical properties of the laterally overgrown aluminum nitride films.

We report homoepitaxial GaN growth on freestanding (11̄00) oriented (M-plane GaN) substrates using low-pressure metalorganic chemical vapor deposition. Scanning electron microscopy, atomic-force microscopy, and photoluminescence were used to study the influence of growth conditions such as the V/III molar ratio and temperature on the surface morphology and optical properties of the epilayers. Optimized growth conditions led to high quality (11̄00) oriented GaN epilayers with a smooth surface morphology and strong band-edge emission. These layers also exhibited strong room temperature stimulated emission under high intensity pulsed optical pumping. Since for III-N materials the (11̄00) crystal orientation is free from piezoelectric or spontaneous polarization electric fields, our work forms the basis for developing high performance III-N optoelectronic devices.

Time-resolved photoluminescence and light-induced transient grating measurements of GaN epilayers show that the photoluminescence decay can be described by two coupled exponential terms and that carrier mobility and lifetime in GaN epilayers are correlated within the model which accounts for nonradiative carrier recombination predominantly at dislocations. The obtained results demonstrate that migration-enhanced metalorganic chemical vapor deposition (MEMOCVD™) allows for growth of high-quality GaN epilayers on sapphire substrates with the dislocation density close to 108cm−2, carrier lifetime as long as 2 ns, and ambipolar diffusion coefficient of 2.1cm2s−1 corresponding to the hole mobility of approximately 40cm2V−1s−1.

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