Current Collapse in AlGaN/GaN HEMT's analyzed by means of 2D device simulation

In this work, we analyze for the first time, by means of 2D numerical device simulations, the influence of surface states on the DC and pulsed characteristics of AlGaN/GaN HEMT’s, and we show that the concomitant presence, at the ungated surface, of polarization induced negative charge and surface hole traps can explain, without invoking any other hypothesis, all dispersive effects in AlGaN/GaN HEMT’s and, in particular, both gate- and drain-lag experiments. In the presence of polarization charge densities of the order of 1013 cm-2, bands are upward bent at the ungated surface and consequently the dynamics of surface states is governed by hole exchange with the valence band.