Low-resistance ohmic contacts with high transparency to p-type GaN have been developed by oxidizing Ni/Au thin films. Compared to the metallic Ni/Au contacts, the oxidized Ni/Au contacts exhibited lower specific contact resistance and much improved transparency. The transparency was from 65% to 80% in the wavelength of 450–550 nm. A specific contact resistance below 1.0×10−4 Ω cm2 was obtained by oxidizing Ni(10 nm)/Au(5 nm) on p-type GaN. The mechanism of low-resistance ohmic contact could be related to the formation of NiO.

A contact has been developed to achieve a low specific contact resistance to p-type GaN. The contact consisted of a bi-layer Ni/Au film deposited on p-type GaN followed by heat treatment in air to transform the metallic Ni into NiO along with an amorphous Ni–Ga–O phase and large Au grains. A specific contact resistance as low as 4.0×10−6 Ω cm2 was obtained at 500 °C. This low value was obtained by the optimization of Ni/Au film thickness and heat treatment temperatures. Below about 400 °C, Ni was not completely oxidized. On the other hand, at temperatures higher than about 600 °C, the specific contact resistance increased because the NiO detached from p-GaN and the amount of amorphous Ni–Ga–O phase formed was more than that of the sample annealed at 500 °C. The mechanism of obtaining low-resistance ohmic contacts for the oxidized Ni/Au films was explained with a model using energy band diagrams of the Au/p-NiO/p-GaN structure.

We have used proton and As + implantation to increase the resistivity of conventional Si (10 -cm) and Si-on-quartz substrates, respectively. High resistivity of 1.6 M-cm is measured that is close to intrinsic Si and semi-insulating GaAs. Very low loss and cross coupling of 6.3 dB/cm and 79 dB/cm (10 m gap) at 20 GHz are measured on these samples, respectively. The very high resistivity and improved rf performance are due to the extremely fast 1 ps carrier lifetime stable even after a 400 C annealing for 1 h. Little negative effect on gate oxide integrity is also observed as evidenced by the comparable stress-induced leakage current and charge-to-breakdown for 30 A oxides.

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We have investigated an alternative electron-beam crystallization method for poly-Si thin-film transistor application. In contrast to the high crystallization temperature and long duration of conventional furnace crystallization, electron-beam crystallization could be performed at a low thermal budget even without substrate heating. It also provides better device characteristics than conventional furnace annealing, including smaller threshold voltage, higher mobility, smaller subthreshold swing, and larger I ON /I OFF ratio. The much smoother surface than the excimer laser annealed sample is also important for further gate oxide integrity and device performance improvement.