In the last decade, the III-N compounds have attracted much interest because of their applications in blue, violet and ultraviolet optoelectronics. Most of the devices and research use sapphire as a substrate for epitaxy of nitrides. However, these epi-structures contain a very high dislocation density induced by the 16% lattice mismatch between GaN and sapphire. In our laboratory, we grow single ...
In this paper we review the developments of producing non-polar (i.e. m-plane and a-plane) and semi-polar (i.e. (20.1)-plane) wafers by ammonothermal method. The growth method and polishing results are described. We succeeded in producing 26 mm × 26 mm non- and semi-polar wafers. These wafers possess outstanding structural and optical properties, with threading dislocation density of the order of ...
We present a novel process for integrating germanium with silicon-on-insulator (SOI) wafers. Germanium is implanted into SOI which is then oxidized, trapping the germanium between the two oxide layers (the grown oxide and the buried oxide). With careful control of the implantation and oxidation conditions this process creates a thin layer (current experiments indicate up to 20-30nm) of almost pure...
We investigated the transition energy levels of the vacancy defects in gallium nitride by means of a hybrid density functional theory approach (DFT). We show that, in contrast to predictions from a recent study on the level of purely local DFT, the inclusion of screened exchange stabilizes the triply positive charge state of the nitrogen vacancy for Fermi energies close to the valence band. On the...
A micromachined AlGaN/GaN high-electron-mobility transistor (HEMT) on a Si substrate with diamondlike carbon/titanium (DLC/Ti) heat-dissipation layers was investigated. Superior thermal conductivity and thermal expansion coefficient similar to that of GaN enabled DLC/Ti to efficiently dissipate the heat of the GaN power HEMT through the Si substrate via holes. This HEMT with DLC design also mainta...
Direct diode lasers have some of the most attractive features of any laser. They are very efficient, compact, wavelength versatile, low cost, and highly reliable. However, the full utilization of direct diode lasers has yet to be realized. The poor quality of diode laser beam itself, directly affect its application ranges, in order to better use of diode laser stack, need a proper correction of op...
The growth condition of thin heavily Mg-doped GaN capping layer and its effect on ohmic contact formation of p-type GaN were investigated. It is confirmed that the excessive Mg doping can effectively enhance the Ni/Au contact to p-GaN after annealing at 550 °C. When the flow rate ratio between Mg and Ga gas sources is 6.4% and the layer width is 25 nm, the capping layer grown at 850 °C exhibits th...
We report the generation of microdischarges in devices composed of microcrystalline diamond. Discharges were generated in device structures with microhollow cathode discharge geometries. One structure consisted of an insulating diamond wafer coated with boron-doped diamond layers on both sides. A second structure consisted of an insulating diamond wafer coated with metal layers on both sides. In e...
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