High performance NiO/β-Ga2O3 heterojunction pn diodes were realized by applying a sputtered p-type NiO film onto a lightly doped n-type β-Ga2O3 epitaxial layer. Taking advantage of the high barrier height against carriers within the pn heterojunction, the demonstrated device exhibited a high breakdown voltage (VB) of 1059 V without optimized electric field management techniques, and before breakdown the reverse leakage current density remained below 1 μA/cm2. Simultaneously, a relatively low specific on-resistance (Ron, sp) of 3.5 mΩ∙cm2 was achieved. The built-in potential of the heterojunction that determined by a capacitance-voltage (C-V) measurement was around 2.4 eV. As discussed in terms of the energy band diagram of a type-II heterojunction, the conduction band and valence band offsets at the NiO/β-Ga2O3 hetero-interface were estimated to be 1.2 and 2.3 eV, respectively.

In this paper, we present a systematic investigation of metal-organic chemical vapor depositiongrown in situ SiN as the gate dielectric and surface passivation for AlGaN/GaN metal insulator semiconductor high electron mobility transistors (MISHEMTs). The dielectric constant and breakdown field of the in situ SiN were extracted from devices with varied gate dielectric thicknesses. Using frequency-dependent capacitance-voltage and parallel conductance methods, we obtained a low trap density of ~3 x 10 ¹² cm ^-2 eV ^-1 at the SiN/AlGaN interface. The MISHEMTs with a source-drain distance of 3 μm show a maximum drain current of 1560 mA/mm and a high on/off current ratio of 10 ⁹ . The device threshold voltage (V _th ) stability was assessed by means of both negative and positive gate stress measurements, as well as temperature-dependent I _D -V _G measurements. We observed a minimal V _th shift of ~0.4 V under both 3000 s gate stress of V _GS = 4 V and up to 200 °C thermal stimulation. Furthermore, combining the in situ SiN with plasma-enhanced chemical vapor deposition SiN, we developed a bilayer passivation scheme for effective suppression of current collapse. Employing the high-quality in situ SiN, we have demonstrated large-area GaN MISHEMTs on Si with a gate width of 20 mm, showing a low off-state leakage of 2 μA/mm at 600 V and a low dynamic/static ON-resistance ratio. The device results show great advantages of employing in situ SiN in D-mode GaN MISHEMTs for high-efficiency power switching applications.

The explosion of mobile data from the internet of things (IoT) is leading to the emergence of 5G technology with dramatic frequency band expansion and efficient band allocations. Along with this, the demand for high‐performance filters for 5G radio frequency (RF) front‐ends keeps growing. The most popular 5G filters are constructed by piezoelectric resonators based on AlN semiconductor. However, AlN possesses a piezoelectric constant d₃₃ lower than 5 pm V⁻¹ and it becomes necessary to develop novel semiconductors with larger piezoelectric constant. In this work, it is shown that strong piezoelectricity exists in ε‐Ga₂O₃. High‐quality phase‐pure ε‐Ga₂O₃ thin films with a relatively low residual stress are prepared. A switching spectroscopy piezoelectric force microscope (SS‐PFM) measurement is carried out and the piezoelectric constant d₃₃ of ε‐Ga₂O₃ is determined to be ≈10.8–11.2 pm V⁻¹, which is twice as large as that of AlN. For the first time, surface acoustic wave (SAW) resonators are demonstrated on the ε‐Ga₂O₃ thin films and different vibration modes resonating in the GHz range are observed. The results suggest that ε‐Ga₂O₃ is a great material candidate for application in piezoelectric devices, thanks to its wide bandgap, strong piezoelectric property, small acoustic impedance, and low residual stress.

Using GaN-on-Si epilayers, for the first time, fully vertical p-i-n diodes are demonstrated after Si substrate removal, transfer, and n-electrode formation at the top of the device. After SiO ₂ sidewall passivation, the vertical p-i-n diodes, with n-GaN facing up, exhibit VON of 3.35 V at 1 A/cm ² , a low differential ON-resistance of 3.3 mΩcm ² at 300 A/cm ² , and a breakdown voltage of 350 V. The corresponding Baliga's figure of merit is 37.0 MW/cm ² , a very good value for GaN-based p-i-n rectifiers grown on Si substrates. The results indicate that fully vertical rectifiers using GaN-on-Si epilayers have great potential in achieving cost-effective GaN devices for high-power and high-voltage applications.

β-Ga₂O₃ Schottky barrier diodes (SBDs) have been fabricated on a bulk (100) β-Ga₂O₃ substrate and tested as X-ray detectors in this study. The devices exhibited good rectification properties, such as a high rectification ratio and a close-to-unity ideality factor. A high photo-to-dark current ratio exceeding 800 was achieved for X-ray detection, which was mainly attributed to the low reverse leakage current in the β-Ga₂O₃ SBDs. Furthermore, transient response of the β-Ga₂O₃ X-ray detectors was investigated, and two different detection mechanisms, photovoltaic and photoconductive, were identified. The results imply the great potential of β-Ga₂O₃ based devices for X-ray detection.

Interface trapping is one of the most notorious effects that limit device performance in GaN-based MIS high electron mobility transistors (MISHEMTs). In this paper, we present a comprehensive study on interface traps in AlGaN/GaN MISHEMTs using low pressure chemical vapor deposition SiNx as gate dielectric. We combined the trapping analysis in MIS diodes and actual MISHEMTs to estimate the interface trap state densities (D11) and their distributions in the device, and to investigate their influence on device electrical properties. Two types of interface traps with different emission time constants, designated as “slow” and “fast” traps, were identified and characterized by means of pulse-mode current-voltage measurements and a frequency dependent conductance method. It was found that “fast” traps located in the device access region could be effectively restrained by passivation using plasma enhanced chemical vapor deposition SiNx. However, “slow” traps, no matter whether located beneath the metal gate or in the access region, were less influenced by passivation. Due to the strong interference of traps in the access region, D11 extraction using the conventional conductance method was not accurate for the lateral GaN-based MIS diodes. A modified small-signal equivalent circuit that includes the impedance of traps in the access region is proposed. Proper passivation for the device access region is essential when using the conductance method for GaN-based MIS devices.