This work adopts interface charge engineering to fabricate normally off metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) on an in situ SiNx/AlGaN/GaN platform using an in situ O3 treatment performed in the atomic layer deposition system. The combination of in situ SiNx passivation and an O3-treated Al2O3/AlGaN gate interface allows the device to provide an excellent breakdown voltage of 1498 V at a low specific on-resistance of 2.02 mΩ cm2. The threshold voltage is increased by 2 V by significantly compensating the net polarization charges by more than five times with O3 treatment as well as reducing the interface traps and improving the high-temperature gate stability. Furthermore, a physical model of fixed charges at the Al2O3/AlGaN interface is established based on dielectric thickness-dependent linear fitting and numerical calculations. The matched device performance and simulated energy band bending elucidate the O3-treated fixed-charge modulation mechanism, providing a practical method for producing normally off GaN MIS-HEMTs.

β-Ga2O3, an emerging wide bandgap semiconductor material, holds significant potential for various applications. However, challenges persist in improving the crystal quality and achieving controllable doping of β-Ga2O3. In particular, the relationship between these factors and the mechanisms behind them are not fully understood. Molecular beam epitaxy (MBE) is viewed as one of the most sophisticated techniques for growing high-quality crystalline films. It also provides a platform for studying the effects of doping and defects in heteroepitaxial β-Ga2O3. In our study, we tackled the issue of Si source passivation during the MBE growth of Si-doped β-Ga2O3. We did this by using an electron beam vaporize module, a departure from the traditional Si effusion cell. Our research extensively explores the correlation between Si doping concentration and film properties. These properties include microstructure, morphology, defects, carrier conductivity, and mobility. The results from these investigations are mutually supportive and indicate that a high density of defects in heteroepitaxial β-Ga2O3 is the primary reason for the challenges in controllable doping and conductivity. These insights are valuable for the ongoing development and enhancement of β-Ga2O3-based device techniques.

In this work, a dramatic reduction in current collapse is achieved in GaN-based high-electron-mobility transistors (HEMTs) using dual-layer SiNx stressor passivation (DSSP), and the related mechanism is proposed. The SiNx compression neutralizes the inherent piezo polarization caused by the lattice mismatch at the heterojunction and effectively mitigates the peak electric field crowding at the drain-side gate edge, as supported by technology computer-aided design simulation. Thus, the inverse piezoelectric effect is suppressed and the trapped charge density is reduced under high electrical stress. As a result, the current collapse effect can be significantly restrained. Upon pulsing (Vg = −6 and Vds = 20 V), the device with DSSP exhibits a negligible current collapse (∼3%), which is significantly lower than the baseline device (∼34%). Moreover, it shows a one-order-of-magnitude reduction in gate leakage and a significant enhancement in gate stability. These results prove that the DSSP process is an attractive technique to facilitate high-reliability GaN-on-Si HEMTs.

The high-k nature of HfO2 makes it a competitive gate oxide for various GaN-based power devices, but the high trap densities at the HfO2/GaN interface have hindered the application. This work was specifically carried out to explore the interface between GaN and ozone-based atomic-layer-deposited HfO2 gate oxide. Furthermore, the GaN surface is preoxidized before gate oxide deposition to prepare an oxygen-rich HfO2/GaN interface. On the preoxidized GaN surface, a sharper HfO2/GaN interface and amorphous HfO2 bulk form during the subsequent deposition, translating to improved electric performance in metal–insulator–semiconductor (MIS) devices. The ozone-based HfO2 shows a high breakdown electric field (∼7 MV/cm) and a high dielectric constant (∼28). Furthermore, the MIS high electron mobility transistors' negligible VTH hysteresis and parallel conductance measurements reflect the ultralow trap densities of the HfO2/GaN interface (<1012 cm−2 eV−1). Therefore, the proposed HfO2 gate oxide scheme offers a promising solution for developing GaN MIS devices.

In this work, a normally-OFF $\beta $ -Ga2O3 MOSFET enabled by charge trapping layer (CTL) is demonstrated for the first time. The CTL consists of Al:HfO $_{x} 1$ :5 and the tunneling barrier (TB) is Al2O3/HfOx/Al2O3 stack. The developed Ga2O3 MOSFET exhibits a wide ${V}_{\text {th}}$ tuning range to normally-OFF operation and a long-lasting retention characteristic of −0.3 V (ten years). The device obtains a breakdown voltage (BV) of 1815 V, showing high reverse blocking capability based on the proposed CTL technique. ${I}$ – ${V}$ and ${C}$ – ${V}$ analyses are carried out under various temperatures to study the mechanism and explore the charge trapping and de-trapping processes. The results indicate a promising method to achieve E-mode operation for Ga2O3 MOSFET with low charge loss and stable ${V}_{\text {th}}$ .

Recess processes for the fabrication of normally-off GaN HEMTs generally compromise devices' on-state performance. In this work, recess-free quasi-normally-off GaN HEMTs with a threshold voltage of 0.24 V is realized by local control of two-dimensional electron gas (2DEG) density. The devices feature a 0.1 μm gate length, SiN _x stress liner, and comb gate. SiN _x liner can provide significant stress to AlGaN/GaN heterostructure in the scaled gate region. The additional stress translates to the additional electric field and depletes the 2DEG in the gate region. As a result, the quasi-normally-off operation is achieved. Furthermore, the comb gate structure is introduced to suppress the short channel effects, supported by TCAD simulation. The quasi-normally-off devices' excellent on-state performances are benchmarked against the normally-off devices reported recently and a p-GaN HEMT purchased from a commercial foundry. The results support strain engineering as a promising technique to pursue the normally-off operation of GaN HEMTs.