We report the studies of AlGaN∕GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) using reactive-sputtered HfO2 as the gate dielectric and the surface passivation layer. X-ray photoemission method reveals a conduction-band offset of 1.71eV for the HfO2∕GaN heterostructure. The dielectric constant of HfO2 is estimated to be 21 by capacitance-voltage measurements. MOS-HEMTs with a 1.5-μm-long gate exhibit a maximum drain current of 830mA∕mm and a peak transconductance of 115mS∕mm, while the gate leakage current is at least five orders of magnitude lower than that of the reference HEMTs. Good surface passivation effects of HfO2 have also been confirmed by pulsed gate measurements, with MOS-HEMTs showing a significant drain current recovery from current collapse observed in HEMTs.

AlGaN/GaN high electron mobility transistors (HEMTs) using HfO 2 as a surface passivation layer and metal-oxide-semiconductor HEMTs (MOS-HEMTs) using HfO 2 as gate oxide have been investigated and compared with the regular HEMTs. In MOS-HEMTs, the HfO 2 gate dielectric is also used for passivation simultaneously. Our measurements have shown that both passivated HEMTs and MOS-HEMTs outperformed the regular HEMTs in dc, high-frequency and pulsed-mode operations, with MOS-HEMTs exhibiting the best characteristics, including the highest drain current, the lowest gate leakage current, the largest gate voltage swing, the highest cut-off frequencies and the best immunity to current collapse. In addition, the decrease in transconductance of MOS-HEMTs relative to HEMTs is as low as 8.7%, most probably a consequence of the high-k value of HfO 2 . Our results thus indicate the great potential of HfO 2 /AlGaN/GaN MOS-HEMTs for high-frequency and high-power applications.

Postimplantation thermal processing of Be in molecular-beam-epitaxy-grown GaN by rapid thermal annealing ͑RTA͒ and pulsed laser annealing ͑PLA͒ was investigated. It has been found that the activation of Be dopants and the repair of implantation-induced defects in GaN films cannot be achieved efficiently by conventional RTA alone. On the other hand, good dopant activation and surface morphology and quality were obtained when the Be-implanted GaN film was annealed by PLA with a 248 nm KrF excimer laser. However, observations of off-resonant micro-Raman and high-resolution x-ray-diffraction spectra indicated that crystal defects and strain resulting from Be implantation were still existent after PLA, which probably degraded the carrier mobility and limited the activation efficiency to some extent. This can be attributed to the shallow penetration depth of the 248 nm laser in GaN, which only repaired the crystal defects in a thin near-surface layer, while the deeper defects were not annealed out well. This situation was significantly improved when the Be-implanted GaN was subjected to a combined process of PLA followed by RTA, which produced good activation of the dopants, good surface morphology, and repaired bulk and surface defects well.

The effects of annealing on the structural properties of radio-frequency sputtered amorphous silicon carbide films prepared under different hydrogen partial pressures (PH) were investigated. Infrared (IR) results of the as-prepared films suggest that as PH increases, more hydrogen is incorporated into the film to form the Si–H and C–H bonds and less silicon and carbon atoms are available to form the Si–C bonds. X-ray photoelectron spectroscopy (XPS) results of the as-prepared films agree with the IR results in that the percent of Si–C decreases and the percent of Si–H and C–H increases as PH increases. IR and XPS results of the annealed films suggest that as the annealing temperature increases, the dangling Si and C bonds will combine to form the Si–C bonds for the unhydrogenated samples. The increase in Si–C bonds for the hydrogenated samples is more likely to be due to the formation of Si–C bonds from the breaking up of the Si–H and C–H bonds.

Tuning of surface plasmon resonance by gold and silver bimetallic thin film and bimetallic dot array is investigated. Laser interference lithography is applied to fabricate the nanostructures. A bimetallic dot structure is obtained by a lift-off procedure after gold and silver thin film deposition by an electron beam evaporator. Surface plasmon behaviors of these films and nanostructures are studied using UV-Vis spectroscopy. It is observed that for gold thin film on quartz substrate, the optical spectral peak is blue shifted when a silver thin film is coated over it. Compared to the plasmon band in single metal gold dot array, the bimetallic nanodot array shows a similar blue shift in its spectral peak. These shifts are both attributed to the interaction between gold and silver atoms. Electromagnetic interaction between gold and silver nanostructures is discussed using a simplified spring model.