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This work demonstrates the advantage of carrying out silicon ion (Si+) implantation at high temperatures for forming controlled heavily doped regions in gallium oxide. Room temperature (RT, 25 °C) and high temperature (HT, 600 °C) Si implants were carried out into MBE grown (010) β-Ga2O3 films to form ∼350 nm deep Si-doped layers with average concentrations up to ∼1.2 × 1020 cm−3. For such high concentrations, the RT sample was too resistive for measurement, but the HT samples had 82.1% Si dopant activation efficiency with a high sheet electron concentration of 3.3 × 1015 cm−2 and an excellent mobility of 92.8 cm2/V·s at room temperature. X-ray diffraction measurements indicate that HT implantation prevents the formation of other Ga2O3 phases and results in reduced structural defects and lattice damage. These results are highly encouraging for achieving ultra-low resistance heavily doped Ga2O3 layers using ion implantation.

Proton irradiation-induced effects on AlGaN/GaN high electron mobility transistors (HEMTs) were studied by emulating a certain space radiation environment (upstream of the earth's bow shock) using a relatively low energy (100 keV) proton beam with fluences of 1 × 1010, 1 × 1012, and 1 × 1014 protons/cm2. In order to isolate radiation-induced effects produced by the modification of the epi-layer from the effects produced by the change in the device structure (such as contacts), the epi-layers were irradiated prior to device fabrication, followed by material/device characterization. Proton irradiation-induced sub-gap traps were detected by spectroscopic photo current-voltage measurement. Raman study revealed that the proton irradiation had induced strain relaxation on the AlGaN/GaN HEMTs epi-layer. No substantial change in the crystal quality of the epi-layer was indicated by Raman and PL studies. With increasing proton fluences, increasing charge carrier density was observed, which was estimated via Raman spectroscopy and the charge-control model analysis. The magnitude and direction of the transistor threshold voltage shift were also dependent on proton fluence. Overall, degradation of transistor output characteristics of the fabricated HEMTs was observed with increasing proton fluence. However, based on the observed performance and the level of influence on material/device characteristics by 100 keV protons, it can be suggested that the AlGaN/GaN HEMTs have high endurance for exposure to relatively high fluences of the low-energy proton beam.

Nitric oxide postoxidation anneal results in a significant decrease of defect state density (Dit) near the conduction bandedge of n-4H–SiC at the oxide/(1120) 4H–SiC interface. Comparison with measurements on the conventional (0001) Si-terminated face shows a similar interface state density following passivation. Medium energy ion scattering provides a quantitative measure of nitrogen incorporation at the SiO2/SiC interface.

Results for measurements of interface state density and breakdown field strength are reported for deposited oxides on n 4H–SiC following passivation with nitric oxide. Low-temperature oxides deposited by plasma-enhanced chemical vapor deposition and high-temperature oxides deposited at 950 °C were investigated. Nitrogen passivation of deposited oxides on n 4H–SiC is found to produce interface state densities of 1–2×1012 cm−2 eV−1 at Ec−E=0.1 eV, regardless of variations in oxide deposition procedures that affect the residual interfacial carbon concentration. Breakdown field strengths were higher for passivated high-temperature oxides compared to passivated low-temperature oxides at room temperature and 290 °C. We suggest that additional oxide growth during the NO passivation is the reason for the observed interface state densities.

Oxidation and silicidation have been found to enhance phosphorus diffusion and incorporation in 4H-SiC. Depth profiling by secondary ion mass spectrometry showed significant concentration of phosphorus in the order of 1018–1019 cm−3 in the near-surface region of 4H-SiC in both oxidation and silicidation-assisted phosphorus-diffused samples. However, silicidation was remarkably more effective than oxidation in promoting phosphorus diffusion, producing comparable phosphorus concentration at even greater depth at a temperature of only 900 °C. Specific contact resistance values of the phosphorus-doped samples confirmed feasibility of this method in ohmic contact fabrication on SiC.

The electrical properties and thermal stability of ZrB2 Schottky contacts deposited on n-type GaN have been studied. As-deposited contacts had a barrier height of 0.80eV, which decreased to 0.7eV after annealing at 300°C, and to 0.6eV after additional annealing at 400°C in nitrogen for 20min. However, the barrier height remained at about 0.6eV even when the diodes were annealed at 600°C for 20min. The Rutherford backscattering spectra of annealed contacts showed no reaction at the ZrB2∕GaN interface. These results make ZrB2∕GaN Schottky contacts attractive for high temperature device applications.

Interface trap passivation at the SiO2∕carbon-terminated (0001¯) face of 4H-SiC utilizing nitridation and hydrogenation has been evaluated. The SiO2∕SiC interface, created by dry thermal oxidation on the C face, shows appreciably higher interface state density near the conduction band compared to the (0001) Si face. A postoxidation anneal in nitric oxide followed by a postmetallization anneal in hydrogen results in dramatic reduction of the trap density by over an order of magnitude near the conduction band. The electrical measurements have been correlated with the interfacial chemistry.