Frequency dependent capacitance of insulator GaN/AlGaN/GaN heterostructure

We explored theoretically and experimentally frequency dependence of capacitance of insulator/GaN/AlGaN/GaN heterostructure MISH (metal insulator semiconductor heterostructure) capacitor and influence of interface traps density present at insulator/GaN/AlGaN interface on capacitance curves. We obtain correspondence between experimental results and theoretical predictions. Depending on the interface traps density the second capacitance step appeared in both theoretical and experimental results. Its position and slope of capacitance increase depend also on interface traps density. Increasing the interface traps density starting from certain density the second capacitance step does not appear and the capacitance curve looks like the capacitance curve of the structure with Schottky diode. For low frequency case, capacitance plateau is higher than for higher frequencies. We may assume that some part of shallower traps is able to respond to the measuring signal and contribute to the total structure capacitance.