GaN power transistors are widely investigated because of their high breakdown voltage, low on-state resistance and fast switching speed. Conventional AlGaN/GaN Schottky high electron mobility transistors (HEMTs) suffer from a high gate leakage and a small gate swing.

By inserting an insulator under gate metal, the MIS-HEMTs are highly preferred over the Schottky-gate HEMTs for high-voltage power switches, owing to the suppressed gate leakage and enlarged gate swing. However, the insertion of the gate dielectric creates an additional dielectric/(Al)GaN interface that presents some great challenges to AlGaN/GaN MIS-HEMTs, such as the threshold voltage (V_th) hysteresis, current collapse and the reliability of the devices.

Recently, Prof. ZHANG Baoshun’s group at Suzhou Institute of Nano-tech and Nano-bionics of Chinese Academy of Sciences presented a fabrication technology of high performance AlGaN/GaN metal-insulator-semiconductor high electron-mobility transistors (MIS-HEMTs) using in-situ pre-deposition plasma nitridation and LPCVD-Si₃N₄ gate insulator. 

The in-situ pre-deposition plasma nitridation process improves the LPCVD-Si₃N₄/GaN interface quality by removing oxygen-related bonds and reducing surface dangling bonds. A high-quality LPCVD-Si₃N₄/GaN_-cap interface was obtained.

The fabricated MIS-HEMTs exhibit a very-low V_th hysteresis of 186 mV at V_G-sweep = (-30 V, +24 V), a high breakdown voltage of 881 V with the substrate grounded. Switching after an off-state V_DS stress of 600 V, the dynamic on-resistance R_on is only 18% larger than the static R_on.

Thus, the LPCVD-Si₃N₄/GaN/AlGaN/GaN MIS-HEMT processes with in-situ pre-deposition plasma nitridation exhibits promising characteristics for power electronic applications. This work was published in IEEE Electron Device Letters.

This work was partly supported by the Key Technologies Support Program of Jiangsu Province, National Natural Science Foundation of China and the National Key Scientific Instrument and Equipment Development Projects of China.