Control of Surface Chemistry in Recess Etching toward Normally Off GaN Metal–Insulator–Semiconductor High‐Electron‐Mobility Transistors

Reducing off‐state and gate leakage current is crucial in the development of metal–insulator–semiconductor high‐electron‐mobility transistors (MIS‐HEMTs). This work reports interface engineering in the gate recess region through low‐damage digital etching during the fabrication of normally off GaN MIS‐HEMTs. Conventional plasma etching leads to a reduction of the N/(Al+Ga) ratio, but this value recovers to almost 1 with optimized oxidation condition during digital etching, suggesting a reduction of the Al/Ga dangling bonds based on the proposed technique. GaN MIS‐HEMTs with digital etching exhibits a threshold voltage of 1.0 V at 1 μA mm−1, a high ON/OFF current ratio of 1010, a gate breakdown voltage of 22 V, and a low gate leakage current of 10−8 mA mm−1. Normally‐off GaN metal‐insulator‐semiconductor high‐electron‐mobility transistor (MIS‐HEMT) was fabricated. With optimized oxidation power, N/(Al+Ga) ratio in the gate recess region recovers to 0.96, identical to that of the pristine HEMT surface, suggesting a reduced number of Al/Ga dangling bonds and lower surface defects. The proposed device exhibits low leakage current and high on/off ratio.