Investigation of surface traps-induced current collapse phenomenon in AlGaN/GaN high electron mobility transistors with schottky gate structures

This paper reports on the studies of current collapse phenomenon induced by surface trapped charges during gate pulse switching in AlGaN/GaN heterostructure high-electron-mobility transistors. A physical-based model, taking into account the distribution features of the applied electric field along the surface of the device barrier layer near the drain-side gate corner, is proposed to analyse the electron trapping and de-trapping processes at the ionized donor-like traps during the device off-state or on-state process. Then the model is analysed and verified by TCAD simulation and laboratory measurement data. The morphology of the current collapse related AlGaN surface is investigated by SEM and AFM characterizations. The dynamic process and quantitative relationship between the electric field and trapped electron density are determined and analysed in detail. The spatial distributions of the trapped electrons and excess free electrons along AlGaN barrier surface are achieved by using the proposed physical model. The work provides a distinct perspective to understand and quantify the current collapse mechanism in AlGaN/GaN power devices, and it can also assist engineers for a better device design. (paper)