Breakdown mechanisms in AlGaN/GaN HEMTs: An overview

This paper reviews the physical mechanisms responsible for breakdown current in AlGaN/GaN high electron mobility transistors (HEMTs). Through a critical comparison between experimental data and previously published results we describe the following mechanisms, which can be responsible for the increase in drain current at high drain voltage levels, in the off-state: (i) source-drain breakdown, due to punch-through effects and/or to a poor depletion of the buffer; (ii) vertical (drain-bulk) breakdown, which can be particularly prominent when the devices are grown on a silicon substrate; (iii) breakdown of the gate-drain junction, due either to surface conduction mechanisms or to conduction through the (reverse-biased) Schottky junction at the gate; (iv) impact ionization triggered by hot electrons, that may induce an increase in drain current due to the lowering of the barrier for the injection of electrons from the source.