Characterization and simulation of AlGaN barrier structure effects in normally-off recessed gate AlGaN/GaN MISHEMTs

The objective of this study is to optimize the trade-off between threshold voltage (V_TH) and maximum drain current (I_D,max) in recessed gate AlGaN/GaN metal insulator semiconductor high electron mobility transistor (MISHEMT) using atomic layer etching (ALE) technology, with technical computer-aided design (TCAD) simulations assisting in the analysis of the underlying mechanisms to demonstrate the high performance and reliability of GaN-based power application. A normally-off recessed gate MISHEMT with varying AlGaN remaining thickness (2 nm, 3 nm, and 5 nm) was fabricated using the ALE process, ensuring precise etch depth and minimal surface damage. The device with a 5 nm AlGaN remaining thickness exhibited excellent performance, with an I_D,max current of 347 mA mm⁻¹, a V_TH of +2.6 V, and a breakdown voltage (BV) of 830 V, compared to the AlGaN barrier with remaining thicknesses of 3 nm and 2 nm, which only reached 120 V and 75 V, respectively. The different recessed gate AlGaN remaining electric field distribution results were verified according to TCAD simulations. This is attributed to the hot electrons effect under the action of the high electric field to promote electrons to overcome potential energy barriers that are injected into a buffer, barrier, or insulating layers and trapped there, degrading off-state BV capability.