Electrical properties of MgO/p-diamond junction fabricated on homoepitaxial single-crystalline diamond

Sufficiently flat and hillock-free insulating homoepitaxial diamond films were successfully grown on high-pressure–high-temperature-synthesized diamond using a 5-kW microwave-plasma chemical-vapor-deposition system with a 20-ppm-nitrogen-included source gas of 4% CH₄ diluted with H₂. Then, layered MgO/boron-doped (p-type) diamond structures were fabricated on the homoepitaxial insulating diamond. Current (I)–voltage (V) characteristics of these device structures showed strong nonlinear behaviors for both current directions, or those for two electrically-parallel, reversed diodes, with conduction limited mainly by sheet resistance of the p-diamond layer in a temperature range from 300 to 600 K. This suggests that the carrier transport occurred through different current passes in the junction region at both biases. Low-frequency capacitances measured were mainly dominated by the depletion capacitance which was influenced by the bias voltage. At relatively high frequencies, however, the total capacitance measured (C) was determined not only by the depletion capacitance but also by the series resistance and the dispersion capacitance. Equivalent circuits of the MgO/p-diamond structure were deduced to explain the measured I–V and C–V results. A possible conduction mechanism is proposed in relation to the electronic structure of the MgO/p-diamond junction.