A novel enhancement-mode GaN vertical MOSFET with double hetero-junction for threshold voltage modulation

A novel Enhancement-mode (E-mode) GaN vertical power MOS transistor (VMOS) with GaN/AlGaN/GaN double heterojunction (DH) is proposed in this work. The polarization effect of the top GaN/AlGaN hetero-junction can be engineered by tailoring the top GaN layer thickness, which enables flexibly modulate the threshold voltage (Vth) of the DH-VMOS. Meanwhile, the two-dimensional electron gas (2-DEG) at the lower AlGaN/GaN hetero-interface performs as part of the conduction channel of the device which is beneficial for device on-resistance (Ron) reduction. By increasing the top GaN layer thickness from 5 to 40 nm the Vth of the DH-VMOS can be shifted from +2.9 to +4 V. The demonstrated device structure presents a novel and controllable approach to modulate the Vth of E-mode GaN vertical power devices, which is of great interests for GaN power device for over kilo-volt applications.