In this paper, a device structure of high-resistivity-cap-layer HEMT (HRCL-HEMT) is developed for normally-off p-GaN gate HEMT toward high breakdown voltage and low current collapse. It demonstrates that the breakdown capability and current collapse of the device were effectively improved due to the introduction of a thick HR-GaN cap layer. The fabricated HRCL-HEMT exhibits a high breakdown voltage of 1020 V at IDS = 10 μA/mm with the substrate grounded. Meanwhile, the dynamic Ron is only 2.4 times the static Ron after off-state VDS stress of 1000 V with the substrate grounded (the OFF to ON switching time interval is set to 200 μs).

We report on the electrical and microstructural characterization of Au-free Ti/Al/Ti/TiN contacts for AlGaN/GaN heterostructures. Ultra-low Au-free ohmic contact has been obtained with contact resistance and specific contact resistivity as low as 0.21 Ω · mm and 1.16 x 10 ^-6 Ω · cm ² , respectively. The ohmic alloy temperature is reduced as low as 550 °C by pre-ohmic recess of the AlGaN barrier and optimization of the thickness of bottom Ti layer. We found that interfacial layer formation of AlN between the ohmic metal and AlGaN surface is crucial to realize a low contact resistance with reduced low annealing temperature by a combination of electrical I-V characterization and high-resolution transmission electron microscopy analysis. Furthermore, we suggest a hypothesis that the bottom Ti layer plays a catalytic role for the Al-N reaction with optimized thickness.

A high-performance quasi-vertical GaN Schottky barrier diode (SBD) was successfully fabricated by using a high-quality n ^- -GaN drift layer with a precisely-controlled n-type doping. A high current on/off ratio of 10 ¹⁰ , an ideality factor of 1.03, a low specific on-resistance of 1.41 mΩ·cm ² , and a relatively high breakdown voltage (BV) of 250 V have been achieved for the SBD without edge termination. Furthermore, with an Argon-implanted termination, the as-fabricated GaN-on-Si SBD shows a record high BV of 405 V, yielding a critical electric field of ~ 2 MV/cm, while the forward conduction characteristics are well maintained.

In this paper, an analytical switching loss model for Gallium Nitride (GaN) based control switch (CS) and synchronous rectifier (SR) in low-voltage buck converters is proposed. Based on the consideration of parasitic inductances, SR reverse conduction voltage drop, and overshoot current effect caused by output capacitance of SR, the total switching loss is modeled with regards to both CS and SR, which can lead to more accurate prediction of power loss and system efficiency in low-voltage buck converters. The modeling results show that the percentage of SR switching loss in total switching loss is 25.4% in the 12-1.2V converter, which is far larger than the 6.3% in the 48-5V converter, and this verifies the necessity of including SR into the model for low-voltage converters. Experiment results exhibit an average increase of 52.3 % and 66.1 % in accuracy of predicted system efficiency and converter power loss through proposed model with SR than conventional models from 400 kHz to 1 MHz.

A high di/dt MOS-controlled thyristor with cathode-short structure (CS-MCT) is developed for pulse power applications. Compared with conventional MCT (con-MCT), the cathode short in the proposed CS-MCT greatly improves the dV/dt robustness. To achieve simultaneously high di/dt capability, special design of device characteristics parameter and consideration of 2-D transient carrier transport are carried out for the first time. Experimental results show that the proposed CS-MCT exhibits di/dt over 357 kA/cm ² /μs and peak current of 27.1 kA/cm ² . Meanwhile, the improved practical dV/dt characteristics are validated in comparison with con-MCT at the same condition. The high di/dt property and simultaneously high dV/dt robustness indicate the proposed CS-MCT is a promising semiconductor pulse switch for pulse power applications.