Device Characteristics of E-mode GaN HEMTs with a Second Gate Connected to the Source

In this study, the device characteristics of dual-gate GaN high-electron-mobility transistors (HEMTs) were determined. The research investigated an enhancement-mode (E-mode) GaN HEMT with a second gate connected to the source and located between the main gate and drain. Two dual-gate GaN HEMTs with different second-gate designs, using Schottky or metal–insulator–semiconductor (MIS) contacts, were simulated and fabricated, and the direct current of the devices was investigated. In device simulation, p-GaN gates were used to achieve E-mode operation in HEMTs. Technology computer-aided design (TCAD) simulation indicated that the saturation drain current (I_{D, sat}) of devices with Schottky and MIS second gates was 88% and 38% lower than that of a single gate structure, while increasing on resistance (R_on) by 31% and 8%, respectively. In device fabrication, a Schottky and MIS second gate were respectively added to an E-mode p-GaN gate HEMT and an E-mode recesses-gate GaN MIS-HEMT. Compared with single-gate structures, the devices with a Schottky and MIS second gates reduced I_{D, sat} by 75% and 32%, respectively, while increasing R_on by 25% and 6%, respectively. The measured electrical characteristics indicate the same trend obtained from TCAD simulation: The dual-gate design can improve the short-circuit capability of GaN HEMTs by reducing the I_{D, sat} under on-state and high-current conditions.