Kurakin A. Radiation effects in HEMTs made on the basis of AlGaN/GaN heterojunctions.

The thesis presents the results of investigation of the effect of гамма-radiation on the parameters and characteristics of device structures made on the basis of AlGaN/GaN heterojunction. For high electron mobility transistors (HEMTs) with channel widths from 100 up to 400 mm and gate lengths from 0.15 up to 0.35 mm, degradation of the main operational parameters (saturation current, cut-off voltage, transconductance) under irradiation (doses up to 2?108 rad) is comprehensively analyzed from I-V curves. From the results of structure investigations performed, the processes occurring in contact metallization of the Au-Ni-GaN and Au-ZrB2-AlGaN/GaN Schottky contacts under irradiation up to a total dose of 2?109 rad are considered. Despite the expected high tolerance of devices made on the basis of nitride group materials, considerable (up to 40%) degradation of the main transistor parameters, as well as complex character of induced degradation of HEMTs, were found (the dependence of the effects on the transistor structure geometry and operation conditions was observed). The physical reasons for radiation aging of test structures are analyzed, with allowance made for possible relaxation of mechanical stresses in the AlGaN barrier layer, enhanced reactions between phases and grain-boundary diffusion in the contact metallization.