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Vertical GaN trench MOSFETs have shown enormous potential for efficient power switching applications. Low ON-resistance ( RON) to minimize power loss, high output current ( ION) to maximize driving capability, and large threshold voltage ( Vth) to avoid false turn-on are highly desirable. This work reports vertical GaN trench MOSFETs with step-graded channel doping. Conventional devices with uniform channel doping were involved for comparison. The experimental results show that step-graded channel doping can achieve an improved trade-off between ION, RON, and Vth than uniform channel doping.

We report high performance ultraviolet (UV) photodetectors (PDs) based on p-GaN-gated AlGaN/GaN heterostructures grown on silicon substrates. Benefitting from the high electrical gain resulting from the transistor-like operation of the device, a photocurrent as high as 4.8 mA/mm was achieved with UV illumination. Due to the effective depletion of the two-dimensional electron gas at the AlGaN/GaN heterointerface via a p-GaN optical gate, the dark current was suppressed to below 3 × 10−8 mA/mm. A high photo-to-dark current ratio over 108 and a high responsivity of 2 × 104 A/W were demonstrated in the device. Moreover, with a cutoff wavelength of 395 nm, the PDs exhibited an ultrahigh UV-to-visible rejection ratio of over 107. Limited by a persistent photoconductivity effect, the rise time and fall time of the device frequency response were measured to be 12.2 ms and 8.9 ms, respectively. The results suggest the potential of the proposed PDs for high-sensitivity UV detection.

We report enhanced gate stack stability in GaN metal insulator semiconductor high electron mobility transistors (MISHEMTs) by using a bilayer SiNx as the gate dielectric. To obtain the bilayer gate dielectric scheme, a thin Si-rich SiNx interlayer was deposited before a high-resistivity SiNx layer by low pressure chemical vapor deposition. The Si-rich SiNx can effectively suppress the trapping phenomenon at the interface of the dielectric/AlGaN barrier. The upper high-resistivity SiNx layer can greatly block the gate leakage current to enable a large gate swing. Compared with the MISHEMTs using a single Si-rich or high-resistivity SiNx layer, the MISHEMTs with a bilayer gate dielectric take the advantages of both, realizing a gate stack with a stable threshold voltage and low leakage current. These results thus present great potential for developing high-performance GaN MISHEMTs using the bilayer SiNx gate dielectric scheme for highly efficient power applications. Published by AIP Publishing.

In this letter, monolithic integration of InGaN/GaN light emitting diodes (LEDs) with vertical metal-oxide-semiconductor field effect transistor (VMOSFET) drivers have been proposed and demonstrated. The VMOSFET was achieved by simply regrowing a p- and n-GaN bilayer on top of a standard LED structure. After fabrication, the VMOSFET is connected with the LED through the conductive n-GaN layer, with no need of extra metal interconnections. The junction-based VMOSFET is inherently an enhancement-mode (E-mode) device with a threshold voltage of 1.6 V. By controlling the gate bias of the VMOSFET, the light intensity emitted from the integrated VMOSFET-LED device could be well modulated, which shows great potential for various applications, including solid-state lighting, micro-displays, and visible light communications.

We report the use of SiNx grown in situ by metal-organic chemical vapor deposition as the gate dielectric for AlN/GaN metal-insulator-semiconductor (MIS) structures. Two kinds of trap states with different time constants were identified and characterized. In particular, the SiNx/AlN interface exhibits remarkably low trap state densities in the range of 1011–1012 cm−2eV−1. Transmission electron microscopy and X-ray photoelectron spectroscopy analyses revealed that the in situ SiNx layer can provide excellent passivation without causing chemical degradation to the AlN surface. These results imply the great potential of in situ SiNx as an effective gate dielectric for AlN/GaN MIS devices.

Structural and electronic properties of Zn-doped cubic boron nitride (cBN) were investigated via first principle calculation based on density functional theory. Our simulation suggests that Zn can substitute for both B (ZnB) and N (ZnN) atom; ZnB is energetically favorable, and ZnN can only be prepared under B-rich conditions. ZnB induced a shallow acceptor level; however, the large difference in electronegativity between Zn and N makes the acceptor level strongly localized, which reduces effective carrier density. In the case of ZnN, both deep acceptor levels within band gap and shallow acceptor levels at the top of valence band were induced, which produced more free carriers than ZnB. The calculated results account for experimental results of enhanced electric conductivity of Zn-doped cBN films prepared under B-rich conditions.

We report an investigation of in situ SiNx gate dielectric grown on AlN/GaN heterostructures by metal-organic chemical vapor deposition. It is revealed that the in situ SiNx is Si-rich, with a N/Si ratio of 1.21 and a relatively high effective dielectric constant of ∼8.3. The 7 nm in situ SiNx film exhibited a large resistivity of >1014 Ω · cm and a breakdown field of 5.7 MV/cm. Furthermore, interface trapping effects in the in situ SiNx/AlN/GaN heterostructures were investigated by frequency dependent conductance analysis.