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We report a high-performance normally-off Al 2 O 3 /AlN/GaN MOS-channel-high electron mobility transistor (MOSC-HEMT) featuring a monocrystalline AlN interfacial layer inserted between the amorphous Al 2 O 3 gate dielectric and the GaN channel. The AlN interfacial layer effectively blocks oxygen from the GaN surface and prevents the formation of detrimental Ga-O bonds. Frequency-dispersion in C-V characteristics and threshold voltage hysteresis are effectively suppressed, owing to improved interface quality. The new MOSC-HEMTs exhibit a maximum drain current of 660 mA/mm, a field-effect mobility of 165 cm 2 /V·s, a high on/off drain current ratio of ~10 10 , and low dynamic on-resistance degradation.

Tunneling induced electron transfer in SiN x /Al 0.22 Ga 0.78 N/GaN based metal–insulator–semiconductor (MIS) structures has been investigated by means of capacitance–voltage (C–V) measurements at various temperatures. Large clock-wise hysteresis window in C–V profiles indicates the injection of electrons from the two-dimensional electron gas (2DEG) channel to the SiN x layer. Depletion of the 2DEG at positive bias in the negative sweeping direction indicates that the charges injected have a long decay time, which was also observed in the recovery process of the capacitance after injection. The tunneling induced electron transfer effect in SiN x /Al 0.22 Ga 0.78 N/GaN based MIS structure opens up a way to design Al x Ga 1− x N/GaN based variable capacitors and memory devices.