Study on electronic properties of diamond/SiNx-coated AlGaN/GaN high electron mobility transistors operating up to 500 °C

We report on the research related to integration and characterization of AIGaN/GaN heterostructure-based circular high electron mobility transistors (c-HEMTs) with diamond thin films. Prior to diamond deposition the transistors were coated by thin SiNx layer in order to protect AlGaN/GaN heterostructure from deposition process impact. The diamond thin film was selectively grown on the top of SiNx-coated c-HEMTs using low-pressure low-temperature microwave plasma deposition equipment with substrate table 20 x 30 cm(2) from C/O/H gas mixture. We demonstrate the functionality of the diamond/SiNx-coated and the SiNx-coated AlGaN/GaN-based c-HEMTs in the temperature range from room temperature to 500 degrees C. The electrical measurements revealed increase of c-HEMTs' leakage currents at reversed gate voltages after diamond deposition, although the transistors remained operable in the tested temperature range. The increase of gate leakage currents and thus more negative pinch-off voltages were attributed to hydrogen penetrated towards AlGaN/GaN interface during the 60 h deposition process despite the SiNx protection. The influence of temperature rise on electronic properties of the diamond/SiNx-coated and the SiNx-coated AlGaN/GaN-based c-HEMTs is discussed.