Reduced interface States of atomic-layer-deposited Al₂O₃/AlGaN/GaN heterostructure containing in situ grown AlN/GaN cap layer and subjected to thermal oxidation

In this study, conventional multiple-frequency capacitance-voltage (C-V) curves of a metal-insulator-semiconductor structure were modified into barrier capacitance-barrier voltage (C_br-V_br) curves to study the interface state of an Al₂O₃/III-N interface. By eliminating the contribution of a serially connected insulator capacitance (C_i), the variation of C_br as a function of V_br could be obtained for determining the interface-state-caused dispersion precisely. This technique was used to deduce the distribution of energy-level-dependent D_it and to investigate the influence of thermal oxidization on an Al₂O₃/AlGaN/GaN heterostructure with an in situ grown AlN/GaN cap layer. The oxidization process was performed prior to Al₂O₃ deposition. Depositing an Al₂O₃ layer on an oxidized wafer by using an atomic layer deposition system can considerably reduce the dispersion behavior among frequencydependent C_br-V_br curves. By determining the amount of frequency dispersion among the C_br-V_br curves, the distribution of Dit was determined to be in the range between 1.4 ×10¹² and 2.6 ×10¹³ eV^-1 ×cm^-2, which was an approximately one-order-of-magnitude reduction compared with a structure that was not subjected to the oxidization process.