This paper reports on the use of low-damage atomic layer etching (ALE) performed using O2 and BCl3 plasma for etching (Al)GaN. The proposed ALE process led to excellent self-limiting etch characteristics with a low direct current (DC) self-bias, which resulted in a high linearity between the etching depth and number of cycles. The etching damage was evaluated using several methods, including atomic force microscopy, photoluminescence (PL), and X-ray photoelectron spectroscopy, and the I–V properties of the recessed Schottky diodes were compared with those of digital etching performed using O2 plasma and HCl solution. The electrical characteristics of the recessed Schottky diode fabricated using the proposed ALE process were superior to those of the diodes fabricated using the conventional digital etching process. Moreover, the ALE process yielded a higher PL intensity and N/(Al + Ga) ratio of the etched AlGaN surface, along with a smoother etched surface.

Recessed MIS gate structures with SiNx gate dielectric layer were investigated for use in normally off AlGaN/GaN‐on‐Si high electron mobility transistors (HEMTs). The channel mobility and threshold voltage (Vth) instability were strongly affected by the recessed configuration. Employing a 30 nm SiNx gate dielectric layer composed of 6 nm PEALD and 24 nm ICP‐CVD films on a 2 nm AlGaN recessed barrier layer resulted in excellent electrical and dynamic characteristics with reduced effective interface trap density. A maximum drain current density of 590 mA mm−1, an on‐resistance of 0.75 mΩ · cm2, and a breakdown voltage of >1100 V were achieved for the gate‐to‐drain distance of 10 μm. Owing to the remaining AlGaN barrier layer under the recessed gate region of the partially recessed device, the interaction between MIS interface traps and channel electrons was suppressed effectively, resulting in improved channel mobility and Vth stability.

A high‐performance E‐mode AlGaN/GaN MIS‐HEMTs is fabricated with atomic layer deposited 5 nm SiON/16 nm HfON and with atomic layer deposited 22 nm HfON gate insulator and their characteristics are compared. Plasma nitridation is employed in every atomic layer deposition cycle to deposit SiON and HfON dielectrics. SiON is used as an interfacial layer to ensure a high‐quality AlGaN/dielectric interface, and high‐k HfON is employed to realize a large transconductance, a high on‐state current, and a high on/off current ratio. The E‐mode AlGaN/GaN MIS‐HEMT with 5 nm SiON/16 nm HfON exhibited more excellent DC and dynamic characteristics than that with 22 nm HfON. The fabricated MIS‐HEMT with dual gate insulator showed a high on/off ratio of ≈1.2 × 1011, a low off‐state drain leakage current less than 10−11 A mm−1, a threshold voltage of 1.1 V, a subthreshold slope of 77 mV dec−1, a specific on‐resistance of 1.34 mΩ cm2, and a breakdown voltage of 800 V.

In this study, we report on the deposition of a highly crystalline AlN interfacial layer on GaN at 330 °C via plasma-enhanced atomic layer deposition (PEALD). Trimethylaluminum (TMA) and NH3 plasma were used as the Al and N precursors, respectively. The crystallinity and mass density of AlN were examined using X-ray diffraction (XRD) and X-ray reflectivity (XRR) measurements, respectively, and the chemical bonding states and atomic concentrations of the AlN were determined by X-ray photoelectron spectroscopy (XPS). The AlN/n-GaN interface characteristics were analyzed using TOF-SIMS and STEM, and the electrical characteristics of the AlN were evaluated using metal-insulator-semiconductor (MIS) capacitors. The PEALD process exhibited high linearity between the AlN thickness and the number of cycles without any incubation period, as well as a low carbon impurity of less than 1% and high crystal quality even at a low deposition temperature of 330 °C. Moreover, the GaN surface oxidation was successfully suppressed by the AlN interfacial layer. Furthermore, enhanced electrical characteristics were achieved by the MIS capacitor with AlN compared to those achieved without AlN.

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