Diamond field-effect transistors for RF power electronics: Novel NO ₂ hole doping and low-temperature deposited Al ₂ O ₃ passivation

Diamond possesses a combination of exceptional physical properties and is expected to be used as a semiconductor material in high-efficiency and high-power electronic devices. In this study, hole doping was observed when using NO 2 molecules on a H-diamond surface. The activation energy of hole concentration in NO 2 /H-diamond was measured as 0.006 eV, and holes were fully activated at room temperature. A thermal stabilization of the hole channel was realized by passivation with an atomic-layer-deposited Al 2 O 3 layer. The passivation method enabled the realization of a thermally stable high-performance diamond field-effect transistor (FET), which exhibited high-performance DC and RF characteristics. NO 2 hole-doping and Al 2 O 3 -passivation technologies enabled reproducible measurements of MOS structure electric properties. Such technologies also facilitated observations of two-dimensional holes at the MOS interface and type-II band alignment of Al 2 O 3 /NO 2 /H-diamond. Additionally, the band diagram under various gate bias conditions was proposed on the basis of capacitance–voltage measurements and analysis using Poisson’s equations.