Electrical Stability of MOS Structures With AlON and Al₂O₃ Dielectrics Deposited on n- and p-Type GaN

This article discusses the electrical stability of MOS structures on n- and p-type GaN for two different dielectrics, AlON and Al2O3, deposited by atomic layer deposition (ALD). Threshold voltage hysteresis was evaluated by means of capacitance-voltage (C-V) double sweep measurements, performed on MOS capacitors. MOS structures on p-doped GaN show up to two orders of magnitude higher effective trapped charge density than on n-GaN. Moreover, AlON results in 10 times less trapped charge than Al2O3 on p-GaN. The leakage current is also identified as an important factor in defining the electrical stability at high electric fields, due to the enhanced injection of electrons into the MOS stack. Electron trapping is shown to happen either at the dielectric-semiconductor interface or in border traps. AlON results in lower flat-band and threshold voltages likely due to the resulting fixed interface charge from surface reconstruction. The effect of the n-type doping density as well as of dry etch damage on the effective trapped charge after injection has been shown to be minimal. These results are important for different insulated gate device architectures. We show that extremely low threshold voltage hysteresis values can be reached in a trench-shaped gate GaN MOSFET using AlON as an interface dielectric.