Normally off operation GaN-based MOSFETs for power electronics applications

Gallium nitride (GaN) is a promising electronic semiconductor material for high-power, high-temperature devices due to its remarkable material properties like wide bandgap, large critical electric field and high saturation velocity compared with Si. The metal-oxide-semiconductor (MOS) field-effect transistor (MOSFET) structure can be operated at a positive threshold voltage, namely the normally off mode, which is preferable for power transistors in terms of fail-safe operation. However in order to minimize the power losses in MOSFET operation, good interface quality at SiO2/GaN and low resistance in the n(+)-contact layer are strongly required. The MOS capacitors were used to characterize the interface states at SiO2/GaN, and the interface state density at E-c - 0.4 eV was less than 1 x 10(11) cm(-2) eV(-1) after annealing at 900 degrees C for 30 min by the furnace. In addition, the activation annealing of Si-implanted GaN was performed at 1260 degrees C for 30 s in rapid thermal annealing (RTA) and its sheet resistance was 23 k Omega sq(-1). Finally, we have fabricated GaN MOSFETs and have achieved more than 1 A operation in the normally off mode at more than 250 degrees C. The breakdown voltage was more than 1500 V. We also confirmed more than 100 h of consecutive operation at 250 degrees C at the moment.