Trapping in Al2O3/GaN MOScaps investigated by fast capacitive techniques

We present a detailed investigation of charge trapping processes in Al2O3/GaN vertical MOS capacitors, detected by means of advanced capacitance measurements. The devices stressed at positive bias present a trapping mechanism that results in an increase of the flatband voltage, while under negative voltages the negative charge stored in bulk and interface states is released with a leftward shift of the C-V characteristic. We also demonstrated that the formation of the hump in depletion regime is the result of trapping of electrons at the oxide-semiconductor interface. The detected behavior is modeled by considering the DIT profile extrapolated by photoassisted CV measurements. The results provide relevant input for the design of stable and reliable MOS transistors based on GaN.