Charge collection mechanisms in AlGaN/GaN MOS high electron mobility transistors

Abstract

Single-event effects (SEEs) in microelectronic devices present a serious reliability concern for space-based applications, where electronic components are exposed to highly energetic ionizing radiation. Single-event effects can be better understood and predicted by investigating the underlying charge collection mechanisms in devices under heavy ion irradiation. Material system and device geometry play a critical role in these mechanisms. High electron mobility transistors (HEMTs) built on the AlGaN/GaN material system are continually being investigated as candidates to meet the ever-increasing demands of high-speed and high-power semiconductor devices. GaN devices have also demonstrated a remarkable tolerance to radiation, but little work has been done to study single-event effects in GaN-based transistors. An investigation of charge collection mechanisms in AlGaN/GaN MOS-HEMTs is presented. Device types include those with no gate oxide, and those with HfO2 and Al2O3 gate oxides. Simultaneous charge collection is observed at the gate and the drain or the source, depending on strike location. Heavy ion data coupled with device simulations show that the introduction of a thin HfO2 layer in the gate stack introduces only a small valence band barrier between the channel and the gate, reducing but not preventing collection of holes at the gate in HfO2-gate devices. Furthermore, an Al2O3 gate oxide increases the valence band barrier over that of the HfO2, to the point where radiation-induced transients are not detectable. These results illustrate the important role that gate oxide material and band alignment play in the charge collection mechanisms of these devices.