Effects of oxygen thermal annealing on AlN trench metal-semiconductor field-effect transistors (MESFETs) on single-crystal AlN substrates

This work reports the demonstration of ultrawide bandgap (UWBG) semiconductor AlN trench metal-semiconductor field-effect transistors, where the impact of oxygen thermal annealing treatment on device electrical properties was comprehensively studied. The gate trench regions were characterized by x-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). XPS results indicated increased Al–O bonding and stronger formation of AlON layer at the surface, while AFM results showed smoother surface morphology after the treatment. Electrical measurements suggested an increase in the Schottky barrier height under the gate and suppressed fast interface trap states after the treatment. Compared with the device without the treatment, the device with the treatment exhibited more than 22 times improvement in on/off ratio and nearly three times enhancement in breakdown voltage due to reduced leakage and improved interface. Temperature-dependent electrical and interface trap characteristics were also measured and compared. This work can serve as an important reference for the development of UWBG AlN transistors for future high-voltage high-temperature electronics.