Simulation of zincblende AlGaN/GaN high electron mobility transistors for normally-off operation

In this work we investigate design parameters enabling normally-off operation of zincblende (ZB-) phase Al_XGa_(1-X)N/GaN high electron mobility transistors (HEMTs) via Synopsys Sentaurus Technology Computer Aided Design (TCAD). As ZB-phase III-nitrides are polarization-free, the 2D electron gas (2DEG) channel at the Al_XGa_(1-X)N/GaN heterojunction is formed through intentional δ-doping part of the Al_XGa_(1-X)N barrier layer. The impact of each of the design parameters (i.e. Al-content and thickness of Al_XGa_(1-X)N barrier; δ-doping location (within the Al_XGa_(1-X)N barrier), δ-doped Al_XGa_(1-X)N layer thickness and its doping amount; gate metal) are studied in detail and design trade-offs are reported. We show that work function of the gate metal impacts normally-off behavior and turn-on voltage considerably. Our results suggest that Al-content of 35% or less in the Al_XGa_(1-X)N barrier results in a normally-off behavior whereas Al_XGa_(1-X)N barrier thickness is effective in controlling the turn-on voltage. Overall, we provide design guidelines in controlling the normally-on/-off operation, threshold voltage, and 2DEG density in ZB-phase AlGaN/GaN HEMT technology.