Selective Growth of GaN pyramids and study of their optical and electronic properties

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GaN and its related compound has given possibilities in the field of optical devices in the region of visible to ultra-violet wavelength as well as electron devices. But almost all the devices so far are on the sapphire substrates. In this study, the selective growth of GaN on a silicon substrate was attempted.(1) Selective growth of hexagonal pyramidal structures and stripe structures were tested on sapphire substrates by MOVPE.In the lateral overgrowth region, unintentional doping of impurities was observed. But the dislocations were found to decline to the horizontal direction and disappeared on the top of the sample.(2) The selective growth of GaN pyramids and stripes was achieved on silicon substrates for the first time. The high quality of the crystal was obtained by controlling the growth conditions for the initial stage of the intermediate layer.(3) An amorphous layer on the order of 5 nm was found between the GaN and the silicon substrate. But the high resolution TEM image showed that the growth of GaN was epitaxal.(4) On the GaN stripe structure, the growth of GaN/AlGaN hetero-structure was attempted, and the micro-sized quantum wells were obtained on silicon substrate for the first time.(5) Selective growth of GaN was attempted on a patterned silicon substrate, which was fabricated by micro-machining technology. Growth of single crystalline GaN of which c-axis is not normal to the substrate surface was achieved for the first time.(6) By reducing the size of window area, the formation of the several seeds was refrained and high quality GaN nano-structure was achieved on silicon substrates.