Gate-Recessed Normally OFF GaN MOSHEMT With High-Temperature Oxidation/Wet Etching Using LPCVD Si3N4as the Mask

Abstract

A gate-recessed normally OFF GaN metal–oxide–semiconductor high-electron-mobility transistor on silicon substrate has been fabricated using a self-terminated, plasma-free oxidation and wet etching process with pre-recess low-pressure chemical vapor deposition (LPCVD) Si3N4 passivation layer. The LPCVD Si3N4 serves the dual role of gate-recess mask and passivation layer. Unlike conventional oxidation etching process using Si3N4 as post gate-recess passivation, the gate channel region was prevented from additional plasma bombardment during the gate window re-opening. As a result, a high-effective channel mobility of 843 $\text {cm}^{\text {2}} / \text {V}\cdot \text {s}$ , and low-channel resistance of $0.89~\Omega \cdot \text {mm}$ are achieved for a normally OFF channel with ${L}_{G} = \text {1.5}\,\,\mu \text{m}$ . For $\text {3}~\mu \text{m}~{L}_{\text {GD}}$ , the fabricated devices exhibit a threshold voltage ( ${V}_{\text {th}}$ ) of 1.35 V, a maximum drain current of ~500 mA/mm, a high ON/ OFF current ratio of ~1010, and 560-V OFF-state breakdown voltage together with a low-forward gate leakage current of ~10−7 mA/mm up to 10 V. A high Baliga’s figure of merit of 1.26 GW/cm2 is achieved in devices with 10- $\mu \text{m}$ gate–drain distance.