Investigation of Defect Distributions in SiO2/AlGaN/GaN High-Electron-Mobility Transistors by Using Capacitance-Voltage Measurement with Resonant Optical Excitation

We investigated the distributions and the energy levels of defects in SiO 2 /AlGaN/GaN highelectron-mobility transistors (HEMTs) by using frequency-dependent ( F - D ) capacitance-voltage ( C - V ) measurements with resonant optical excitation. A Schottky barrier (SB) and a metal-oxidesemiconductor (MOS) HEMT were prepared to compare the effects of defects in their respective layers. We also investigated the effects of those layers on the threshold voltage ( V th ). A drastic voltage shift in the C - V curve at higher frequencies was caused by the large number of defect levels in the SiO 2 /GaN interface. A significant shift in V th with additional light illumination was observed due to a charging of the defect states in the SiO 2 /GaN interface. The voltage shifts were attributed to the detrapping of defect states at the SiO 2 /GaN interface.