Pattern dependent lateral epitaxial overgrowth of gallium nitride by metalorganic chemical vapor deposition

Lateral epitaxial overgrowth (LEO) of GaN, with pattern sizes from the micron-meter scale to the nano-meter scale have been studied by metalorganic chemical vapor deposition and with various analysis techniques such as cathodoluminescence, atomic force microscopy, X-ray diffraction and scanning electron microscopy. The effects of V/III ratio, growth temperature, growth time and pattern fill-factor on the morphology and the lateral growth rate of LEO GaN stripes have been studied in this thesis. NH₃ flow modulation was introduced in the LEO process to obtain the rectangular stripes and increase the lateral growth rate of GaN stripes. Direct LEO on sapphire substrates based on a sparse nucleation process was also investigated. LEO at the sub-micron scale demonstrated many advantages over the micron-scale LEO in the terms of early coalescence, minimal wing-tilt and no threading dislocation (TD) generation at the coalescence front. Selective area growth and LEO at the nano-meter scale on both the GaN and the Si(111) substrates were also demonstrated. The selectivity and uniformity of nanometer sized deposits strongly depend on the growth rate at the growth temperatures attempted.; Time-resolved CL was used to study the carrier relaxation mechanisms in the InGaN/GaN QWs grown on both GaN buffer layers and LEO GaN stripes. On highly defective GaN buffer layers, the QWs show strong carrier localization that is attributed to indium composition fluctuations. Owing to the reduction of TD density and indium composition fluctuations, the InGaN/GaN QWs grown on LEO GaN stripes always show strong and uniform luminescence. It was also found that indium tends to migrate from the sidewalls to the top of GaN stripes. This phenomenon might provide the possibility of fabricating nitride low dimensional quantum structures. InGaN/GaN buried heterostructures (BH) using LEO procedures demonstrates strong and uniform QW luminescence. The atomically smooth waveguide provided by the inclined sidewalls, the electron confinement due to the spatial variation of the QW energy on the sidewalls and stripe top, and the reduced TD density on the mesa top make the BH very attractive for future fabrication of GaN based laser diodes.