Physics-based simulation of field-plate effects on breakdown characteristics in AlGaN/GaN HEMTs

We perform two-dimensional analysis of breakdown characteristics in field-plate AlGaN/GaN HEMTs with a short gate length and a short gate-to-drain distance. It is shown that when an acceptor density in a buffer layer is high, the breakdown voltage is determined by impact ionization of carriers, and it can decrease with increasing the field-plate length. On the other hand, when the acceptor density is relatively low, the buffer leakage current becomes very large and it can determine the breakdown voltage, which becomes very low. In this case, the breakdown voltage increases with increasing the field-plate length.