Three different insulator layers SiN_x, SiON, and SiO₂ were used as a gate dielectric and passivation layer in AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMT). The SiN_x, SiON, and SiO₂ were deposited by a plasma-enhanced chemical vapor deposition (PECVD) system. Great differences in the gate leakage current, breakdown voltage, interface traps, and current collapse were observed. The SiON MIS-HEMT exhibited the highest breakdown voltage and I_on/I_off ratio. The SiN_x MIS-HEMT performed well in current collapse but exhibited the highest gate leakage current density. The SiO₂ MIS-HEMT possessed the lowest gate leakage current density but suffered from the early breakdown of the metal–insulator–semiconductor (MIS) diode. As for interface traps, the SiN_x MIS-HEMT has the largest shallow trap density and the lowest deep trap density. The SiO₂ MIS-HEMT has the largest deep trap density. The factors causing current collapse were confirmed by Photoluminescence (PL) spectra. Based on the direct current (DC) characteristics, SiN_x and SiON both have advantages and disadvantages.

A 2-D simulation of off-state breakdown voltage (V_BD) for AlGaN/GaN high electron mobility transistors (HEMTs) with multi field-plates (FPs) is presented in this paper. The effect of geometrical variables of FP and insulator layer on electric field distribution and V_BD are investigated systematically. The FPs can modulate the potential lines and distribution of an electric field, and the insulator layer would influence the modulation effect of FPs. In addition, we designed a structure of HEMT which simultaneously contains gate FP, source FP and drain FP. It is found that the V_BD of AlGaN/GaN HEMTs can be improved greatly with the corporation of gate FP, source FP and drain FP. We achieved the highest V_BD in the HEMT contained with three FPs by optimizing the structural parameters including length of FPs, thickness of FPs, and insulator layer. For HEMT with three FPs, FP-S alleviates the concentration of the electric field more effectively. When the length of the source FP is 24 μm and the insulator thickness between the FP-S and the AlGaN surface is 1950 nm, corresponding to the average electric field of about 3 MV/cm at the channel, V_BD reaches 2200 V. More importantly, the 2D simulation model is based on a real HMET device and will provide guidance for the design of a practical device.

We demonstrate enhancement of light extraction efficiency (LEE) of gallium-nitride (GaN)- based green light-emitting diode (LED) through a nano- micro complex patterned sapphire substrate (NMCPSS). The NMCPSS was prepared by inductively coupled plasma etching conventional microscale patterned sapphire substrate (PSS) with nickel nano-particles as the mask. The effect of NMCPSS on light output power of GaN-based green LED was investigated experimentally and numerically. The light output power at 20 mA of the LED grown on NMCPSS is 28.6% higher than that of LED grown on PSS. This is close to the value of 33.3% predicted by simulation. The results show that nano-micro complex PSS can further promote the LEE of GaN-based green LED compared to conventional PSS.

We propose the Ti/Al/Ni/Ti ohmic contacts to improve the breakdown voltage (V _BD ) of GaN-based high electron mobility transistors (HEMTs). Using the same photolithography process, the first Ti/Al metal stack and the second Ni/Ti metal stack were achieved by electron beam (EB) evaporation and magnetron sputter, respectively. Attributed to the better particle filling on the sidewall by magnetron sputtering, the second Ni/Ti metal stack completely wraps the first Ti/Al metal stack and extends to both sides after a lift-off process. Even after high temperature annealing (HTA), the Ti/Al/Ni/Ti metal stack can keep smooth edge acuity and surface morphology, resulting in a uniform electric-field distribution near the ohmic contacts. Compared with Ti/Al/Ni/Au ohmic contacts, HEMTs with Ti/Al/Ni/Ti ohmic contacts have higher V _BD and can improve the uniformity as well as repeatability of V _BD .

We fabricated a complex transparent conductive electrode (TCE) based on Ga₂O₃ for AlGaN-based ultraviolet light-emitting diodes. The complex TCE consists of a 10 nm ITO, a 15 nm Ga₂O₃, a 7 nm Ag, and a 15 nm Ga₂O₃, forming a ITO/Ga₂O₃/Ag/Ga₂O₃ multilayer. The metal layer embedded into Ga₂O₃ and the thin ITO contact layer improves current spreading and electrode contact properties. It is found that the ITO/Ga₂O₃/Ag/Ga₂O₃ multilayer can reach a 92.8% transmittance at 365 nm and a specific contact resistance of 10⁻³ Ω·cm² with suitable annealing conditions.