Current collapse-free i-GaN/AlGaN/GaN high-electron-mobility transistors with and without surface passivation

Drain current (I_D) collapse-free i-GaN/AlGaN/GaN high-electron-mobility transistors (HEMTs) with and without surface passivation (electron-beam evaporated SiO₂) were demonstrated using dc and pulsed (120 Hz) I_Ds-V_DS characteristics up to the drain supply voltage of 40V. The observation of small I_D transients and negligibly small hysteresis widths with small white light illumination effects on both passivated and unpassivated i-GaN/AlGaN/GaN HEMTs confirms the suppression of collapse related traps. Three and two thermally activated trap levels were observed in passivated (+0.395, -0.079, and -0.949 eV) and unpassivated (-0.066 and -0.368 eV) AlGaN/GaN HEMTs, respectively. However, I-GaN/AlGaN/GaN HEMTs with and without surface passivation exhibited only one trap level at -0.161 eV. These results show that the addition of thin cap layer i-GaN screens the collapse-related surface states/traps from channel.