Optimization of enhancement-mode MIS-GaN HEMT with dual channel for simple process using TCAD simulation

A metal-insulator-semiconductor (MIS) GaN high electron mobility transistor (HEMT) utilizing a dual-channel structure is demonstrated for enhancement-mode (E-mode) operation using the Synopsys Sentaurus™ technology computer-aided design (TCAD) simulator. The MIS dual-channel HEMT (IDC-HEMT) employs two AlGaN/GaN heterojunction layers to form two two-dimensional electron gas (2DEG) layers. Electrons in the lower 2DEG layer induce a continuous negative bias body effect on the upper channel, shifting the threshold voltage (V_th) in the positive direction and enabling E-mode operation. This structure achieves E-mode operation without requiring additional complex fabrication steps, such as the precise etching processes used in recessed gate or p-GaN gate designs. The 2DEG sheet density in the upper 2DEG of the MIS single-channel HEMT (ISC-HEMT) and IDC-HEMT are 5.49 × 10¹² cm^- 2 and 3.43 × 10¹² cm^- 2, respectively, while the lower 2DEG in the IDC-HEMT has sheet density of 0.76 × 10¹² cm^- 2, all obtained in the access region with a gate and drain bias of 0 V. Due to the reduced 2DEG sheet density in the upper 2DEG, the proposed IDC-HEMT exhibits degraded performance in on-resistance (R_on), with values 28.7 Ω∙mm, respectively, compared to the ISC-HEMT, which has and a R_on of 22.7 Ω mm. However, the V_th of the ISC-HEMT is - 1.41 V, while that of the IDC-HEMT is 0.25 V, demonstrating a significant positive shift of 1.66 V. This confirms that the proposed IDC-HEMT can operate in E-mode.