In this study, we proposed a rectifying drain electrode that was embedded in a p-GaN gate AlGaN/GaN heterojunction field-effect transistor to achieve the unidirectional switching characteristics, without the need for a separate reverse blocking device or an additional process step. The rectifying drain electrode was implemented while using an embedded p-GaN gating electrode that was placed in front of the ohmic drain electrode. The embedded p-GaN gating electrode and the ohmic drain electrode are electrically shorted to each other. The concept was validated by technology computer aided design (TCAD) simulation along with an equivalent circuit, and the proposed device was demonstrated experimentally. The fabricated device exhibited the unidirectional characteristics successfully, with a threshold voltage of ~2 V, a maximum current density of ~100 mA/mm, and a forward drain turn-on voltage of ~2 V.

We utilized a plasma-enhanced atomic layer deposition (PEALD) process to deposit an AlN passivation layer on AlGaN/GaN surface to enhance the polarization effects, which enabled the fabrication of an enhancement-mode (E-mode) AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistor (MIS-HFET) without the need for a gate recess process. The AlN film deposited by PEALD exhibited a crystalline structure, not an amorphous one. The enhanced polarization effect of introducing the PEALD AlN film on a thin AlGaN barrier was confirmed through electrical analysis. To fabricate the E-mode AlGaN/GaN MIS-HFET, the PEALD AlN film was deposited on a 4.5 nm AlGaN barrier layer and then a damage-free wet etching process was used to open the gate region. The MIS-gate structure was formed by depositing a 15 nm plasma-enhanced chemical vapor deposition (PECVD) silicon dioxide (SiO2) film. The fabricated thin-AlGaN/GaN MIS-HFET demonstrated successful E-mode operation, with a threshold voltage of 0.45 V, an on/off ratio of approximately 109, a specific on-resistance of 7.1 mΩ·cm2, and an off-state breakdown voltage exceeding 1100 V.