p-GaN hybrid anode AlGaN/GaN diode with 1000 V operation

Abstract

GaN plays an important role in compound semiconductor, which exhibits excellent electrical properties such as wide band gap (3.4 eV), high breakdown field strength (3.3 MV/cm), and high electron mobility (600 cm2/(Vs)). AlGaN/GaN heterojunction produces two-dimensional electron gas (2DEG) with high density (11013 cm-2) and high electron mobility (2000 cm2/(Vs)) which are caused by strong piezoelectric and spontaneous polarization. The Si-based AlGaN/GaN devices emerge as a promising candidate for the nextgeneration switching application in power system due to 2DEG of AlGaN/GaN heterojunction. Turn-on and breakdown voltage are key parameters for diodes and they have a tradeoff between each other. These two parameters affect diode loss and power handling capability. For better properties, we propose a novel p-GaN hybrid anode AlGaN/GaN diode with high-resistance-cap-layer (HRCL) to optimize turn-on voltage and breakdown characteristics. Based on the p-GaN/AlGaN/GaN material structure, an HRCL is fabricated in the channel region by self-aligned hydrogen plasma treatment to improve the breakdown voltage. Hydrogen plasma is adopted to compensate for holes in the p-GaN to release electrons from the 2DEG channel, forming a high-resistivity area. The transmission line method tests the material after passivation, showing that its sheet resistance is 570 /□ and a contact resistance is 0.7 mm. In the HRCL p-GaN diode, negative charges can appear at the interface of HR-GaN/AlGaN due to polarization effect, which increases the vertical electric field in AlGaN and reduces the lateral electric field near the cathode in the p-GaN, compared with in the p-GaN diode without HRCL. The p-GaN in the anode region is reserved to regulate the turn-on voltage by depleting the underlying 2DEG. The p-GaN structure raises conduction band beyond the Fermi level, ensuring the reduction of 2DEG. The fabricated HRCL p-GaN diode exhibits a high breakdown voltage over 1000 V at Ileakage=110-4 A/mm with a cathode-anode distance Lac of 10 m and a turn-on voltage of +1.2 V when forward current is 1 mA/mm. These results indicate that the introduction of p-GaN hybrid anode and HRCL can enhance the electrical properties of AlGaN/GaN diode effectively. However, little attention has been paid to doping concentration in p-GaN. Study of the regulation of Mg2+ doping concentration on the turn-on voltage in p-GaN will be investigated in future to achieve a low forward turn-on voltage of the p-GaN HRCL diode.