| dc.description.abstract | GaN was grown on Si with the buffer layer of ZnO nanorods arrays (ZnO NRAs) by metalorganic chemical vapor deposition (MOCVD). The lattice mismatch between GaN and ZnO is only 1.85% and the ZnO NRAs buffer is employed to reduce strain energy in the epilayer. We aim to achieve the next-generation GaN crystal with advantages of low cost, large scale, and high qualities. Nevertheless, many challenges remain to be overcome, such as H2 back-etching of ZnO NRAs, thermal decomposition of ZnO, the difficult coalesce of GaN, etc.
The major fabrication procedure of ZnO NRAs consists of two steps: (1) ZnO seed layer deposition (2) hydrothermal process (HTP). The textured ZnO film was deposited on Silicon (100) substrates by radio-frequency sputter (RF-Sputter). Post-annealing of the sputtered ZnO layer is found be vitally important to the morphology of ZnO NRAs, such as diameters, densities, shapes, and tilting angles.
In the growth of GaN, low-temperature (< 600 °C) GaN (LT-GaN) in N2 ambiance is adopted to form the ZnO-GaN core-shell structure in order to prevent the back etching of NRAs at high temperatures. The growth temperature of GaN is then raised to 950 °C to horizontally connect every nanorod and to provide further protection of ZnO. Finally, high-quality GaN is grown at 1120 °C in H2. Before the growth of high-temperature GaN (HT-GaN), a thin layer of high-temperature (also at 1120 °C) AlN (HT-AlN) is used to assist the coalescence of GaN. Although the HT-GaN epilayer reaches the thickness of 2 μm without showing peeling-off and cracks, the crystal still remains uncoalescent. In the Future, optimization of the growth parameters for each layer, including duration, V/III ratios and reactor pressure, should be performed in order to improve the surface morphology of GaN grown with this novel technology. | en_US |