The effects of γ-ray irradiation on AlGaN/GaN epitaxial layers and on high electron mobility transistor (HEMT) devices have been systematically investigated. The layer structure and HEMT device has been irradiated cumulatively with γ-ray dose of the order of 16 kGy. The x-ray diffraction (XRD) analysis of irradiated sample shows a lowering in full width at half maximum (FWHM) values along (102) and (002) planes in comparison to the pristine sample due to partial annealing effect. A decrease in the in-plane biaxial stress from 1.20 GPa to 0.75 GPa has been observed. Raman spectrum analysis also corroborates the reduction in stress post γ-ray irradiation. Edge dislocation density is reduced from 2.7×10 8 cm −2 to 1.75×10 8 cm −2 whereas the screw dislocation density remains almost unaffected. Further, Hall measurement shows an improvement in the mobility from 1580 cm 2 V −1 s −1 to 2070 cm 2 V −1 s −1 with reduction in sheet resistance. This improvement in mobility is attributed due to the decrease in surface roughness as confirmed by atomic force microscopy (AFM) characterization and also due to re-arrangement of the local defect centers as confirmed by cathodoluminescence (CL) imaging analysis. Finally, an increase in drain current from 99.5 mA mm −1 to 121.2 mA mm −1 with reduction in leakage current has been observed in case of HEMT device due to the improvement found in various material parameters.

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This paper presents the electrical comparison of Au and Ni/Au gated HEMT devices and diodes. Au Schottky diodes on an AlGaN/GaN heterostructure exhibit better electrical performance in comparison to conventional Ni/Au diodes with an improved Schottky barrier height (SBH) and lower reverse leakage current. The SBH extracted from I-V for Au and Ni/Au is 1.29 eV and 0.74 eV, respectively. Au Schottky contacts on GaN have a better ideality factor of 1.55 than Ni, which is 1.61. Capacitance-voltage measurement revealed a positive shift in threshold voltage in the case of Au diodes with a reduced capacitance value with respect to Ni/Au diodes. This decrease in threshold and capacitance indicates a decrease in the 2DEG carrier concentration. The decrease in the 2DEG carrier concentration is consistent with three terminal device measurements. Despite a small decrease in drain current (8%), the Au gated HEMT devices have shown an improved subthreshold slope (13%) and nearly 4 order improvement in the ION/IOFF ratio than Ni/Au gated HEMTs. Pulse IV characterization has indicated that gate lag and drain lag have no major changes with respect to gate metal, whereas current collapse increases for high work function metals.

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