Leakage Current Mechanism of InN-Based Metal-Insulator-Semiconductor Structures with Al^sub 2^O3 as Dielectric Layers

InN-based metal-insulator-semiconductor (MIS) structures were prepared with Al^sub 2^O3 as the gate oxides. Surface morphologies of InN films are improved with increasing Mg doping concentrations. At high frequencies, the measured capacitance densities deviate from the real ones with turning frequencies inversely proportional to series resistances. An ultralow leakage current density of 1.35×10^sup -9^ A/cm^sup 2^ at 1 V is obtained. Fowler-Nordheim tunneling is the main mechanism of the leakage current at high fields, while Schottky emission dominates at low fields. Capacitance densities shift with different biases, indicating that the InN-based MIS structures can serve as potential candidates for MIS field-effect transistors.