Effect of γ-ray irradiation on Schottky and ohmic contacts on AlGaN/GaN hetero-structures
Abstract The effect of γ-ray irradiation on the electrical transport characteristics of ohmic contacts and Schottky contacts having different dimensions on AlGaN/GaN hetero-structures has been reported. The contacts have been irradiated with three incremental doses of gamma irradiation up to the order of 104 Gray (Gy). The contacts are electrically characterized using current-voltage (I-V) analysis and the transfer length method (TLM). After each γ-ray dose, both the forward and reverse I-V characteristics show a gradual change associated with the variation in the dimensions of the Schottky contacts. A shift in the turn-on voltage (VF) with a tendency of improvement in the ideality factor (η) and decrease in series resistance(R) of the diode was observed whereas no change in Schottky barrier height (фB) was calculated. The reverse leakage current (IR) was reduced from 27 μA to 10 μA and the contact resistance (RC) value was reduced to 0.35 Ω-mm from 0.7 Ω-mm following the γ-ray irradiation. The Schottky contacts with larger dimensions and lower perimeter-to-area ratios (P/A) showed greater changes in the device parameters (VF, η, IR) due to high induced local heating. X-ray diffraction (XRD) analysis also shows reduction in dislocation density due to partial annealing effect. Finally, capacitance voltage (CV) characterization and Hall measurement shows no change in carrier concentration whereas improvement in the mobility has been observed due to traps/defects redistribution.