This study investigated the effects of a thin aluminum oxynitride (AlO_xN_y) gate insulator on the electrical characteristics of AlGaN/GaN-on-SiC metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs). The fabricated AlGaN/GaN-on-SiC MIS-HEMTs exhibited a significant reduction in gate leakage and off-state drain currents in comparison with the conventional Schottky-gate HEMTs, thus enhancing the breakdown voltage. The effects of gate recess were also investigated while using recessed MIS-HEMT configuration. The Johnson’s figures of merit (= f_T × BV_gd) for the fabricated MIS-HEMTs were found to be in the range of 5.57 to 10.76 THz·V, which is the state-of-the-art values for GaN-based HEMTs without a field plate. Various characterization methods were used to investigate the quality of the MIS and the recessed MIS interface.

We developed a high-quality plasma enhanced atomic layer deposited (PEALD) aluminum oxynitride (AlO _x N _y ) process for the metal-oxide-semiconductor (MOS) gate insulator of fully-recessed-gate AlGaN/GaN-on-Si MOS-heterojunction field-effect transistors (MOS-HFETs). It was found that the cyclic nitrogen incorporation into aluminum oxide (Al ₂ O ₃ ) during PEALD process improved the conduction band offset at GaN interface resulting in higher forward breakdown field strength, which also contributed to suppressed trapping effects under forward gate bias stress. Improved interface characteristics, which resulted from suppressed surface oxidation, led to significant improvement of threshold voltage stability. A low threshold voltage hysteresis of 180 mV at maximum gate sweep voltage of 10 V was obtained with AlO _x N _y gate insulator. The MOS channel mobility was also improved to 235 cm ² V ⁻¹ s ⁻¹ . The fabricated fully-recessed-gate AlGaN/GaN-on-Si MOS-HFET with PEALD AlO _x N _y gate insulator exhibited excellent overall performances such as a threshold voltage of 3.2 V, a maximum drain current density of 481 mA mm ⁻¹ , an on/off current ratio of ∼10 ¹⁰ , an ON-resistance of 12 mΩ mm, and a breakdown voltage of 1050 V.

We optimized a silicon nitride (SiN_x) passivation process using a catalytic-chemical vapor deposition (Cat-CVD) system to suppress the current collapse phenomenon of AlGaN/GaN-on-Si high electron mobility transistors (HEMTs). The optimized Cat-CVD SiN_x film exhibited a high film density of 2.7 g/cm³ with a low wet etch rate (buffered oxide etchant (BOE) 10:1) of 2 nm/min and a breakdown field of 8.2 MV/cm. The AlGaN/GaN-on-Si HEMT fabricated by the optimized Cat-CVD SiN_x passivation process, which had a gate length of 1.5 μm and a source-to-drain distance of 6 μm, exhibited the maximum drain current density of 670 mA/mm and the maximum transconductance of 162 mS/mm with negligible hysteresis. We found that the optimized SiN_x film had positive charges, which were responsible for suppressing the current collapse phenomenon.

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.

This letter reports high-quality plasma-assisted atomic-layer-deposited HfO _x N _y by using isopropyl alcohol (IPA) oxidant and cyclic N ₂ plasma treatment demonstrated on n-type In _0.53 Ga _0.47 As. Improved interface characteristics, with suppressed frequency dispersion and surface oxidation, were demonstrated and resulted in significantly decreased interface trap density ( ${D} _{\text {it}}$ ) of ${4.5}\times {10}^{{11}}$ eV ⁻¹ cm ⁻² at the mid-gap level with outstanding inversion behaviors. In addition, to verify true inversion, transition frequency ( $\omega _{\text{m}}$ ) of 4 kHz was extracted. The improvement mechanism of the proposed technology is assumed to be that nitrogen plasma reduces oxygen vacancies that act as oxygen diffusion paths and with the use of IPA oxidant the interface would be strongly protected during pre- and post-dielectric deposition.