Conductivity Enhancement Induced by Confined Vicinal Hole Storage in Enhancement-mode $p$-GaN Gate Double-Channel HEMTs

We present an enhancement-mode (E-mode) $p$-GaN gate high-electron-mobility transistor (HEMT) featuring a double-channel (DC) structure. An AlN layer (1 nm) inserted at 6 nm below the conventional $p$-GaN/AlGaN/AlN/GaN heterojunction enables the simultaneous formation of a second lower two-dimensional electron gas (2DEG) channel and a barrier layer that can block and confine holes injected from the overlaying $p$-GaN gate at sufficiently large positive gate bias. The injected holes are confined in close vicinity between the upper and lower channels yet are spatially separated from electrons to prolong the minority (i.e., hole) lifetime, which is otherwise very short in the direct-bandgap GaN. Such vicinal hole storage (VHS) can induce more electrons in 2DEG channels, leading to clear enhancement of conductivity. The VHS and its impact on enhanced channel conductivity are also evidenced by simulation results.