Weak Frequency Dispersion of C-V Characteristics of AlGaN/GaN Metal-Insulator-Semiconductor Devices Despite High Interface Trap Density

For AlGaN/GaN metal-insulator-semiconductor (MIS) devices, it is shown that there is a case where the frequency dispersion of the capacitance-voltage (C-V) characteristics is very weak despite a rather high insulator-semiconductor interface trap density. We fabricated metal/Al2O3/AlGaN/GaN MIS devices, and carried out C-V characterization of them. Although they exhibit very weak C-V frequency dispersion for 100 Hz-1 MHz, we found that, based on the conductance method, the insulator-semiconductor interface trap densities are rather high approximate to 3 x 1013 cm-2 eV-1. As a possible explanation, a double-peak model is considered, which underlines the possibility that a high interface trap density does not necessarily lead to strong C-V frequency dispersion. The model can explain the observed weak C-V frequency dispersion, implying that it is not appropriate to naively discuss the interface traps only from the apparent C-V frequency dispersion.