Analysis of Al2O3/diamond interface with high temperature (400 °C) capacitance-voltage method in wide frequency range

Abstract In our previous work, we demonstrated the world's first inversion-type p-channel diamond metal–oxide–semiconductor field-effect transistor (MOSFET). However, it exhibited low channel mobility due to high interface state density (Dit). In this study, the electronic states of Al2O3/diamond interfaces above the valence band edge (Ev) were carefully examined by capacitance–voltage (C–V) measurements in a wide frequency range of 1 Hz–10 MHz at 300, 350, and 400 K, providing an accurate characterization of deeper interface state density compared with our previous work (from 10 Hz to 10 kHz at room temperature) within the limitations of the high-low method. We observed humps in C–V curves, which became wider as the temperature increased and the frequency decreased, indicating the presence of interface states at deep energy levels. They can act as Coulomb scattering centers in diamond MOSFETs; thus, their characterization at low frequencies and high temperatures is necessary. The energy distribution of Dit was estimated using the high-low method at 400 K, indicating that Dit was in the range of (0.4–1.5) × 1012 cm−2eV−1 within 0.23–0.76 eV from Ev of diamond. More effective passivation techniques are required to reduce interface states at deep energy levels.