Electrical Characterization of Metal/AlO/SiO/Oxidized-Si-Terminated (C-Si-O) Diamond Capacitors

Metal-oxide-semiconductor (MOS) capacitors with oxidized silicon-terminated (C-Si-O) diamond as semiconductors and a stack of SiO2 and Al2O3 as gate insulators were successfully fabricated and electrically characterized for the first time. C-Si diamond was first formed by the molecular beam deposition of a Si film and subsequent in situ vacuum annealing. The diamond surface turned into C-Si-O when exposed to the air, accompanying a naturally grown SiO2 film on top. The MOS capacitors exhibited an excellent electrical insulation capability for gate voltages of depletion and accumulation conditions. A dip specific to deep dopants in the substrate was observed for the first time in high-frequency capacitance-voltage ( {C} - {V} ) characteristics of diamond MOS capacitors. In the high-frequency {C} - {V} curve, accurate estimation of flat-band voltage was realized by locating it at the observed dip. Additionally, the margin of error of the flat-band voltage estimated using a conventional method of fitting a Mott-Schottky plot to experimental {C} - {V} curves was assessed and attributed to the neglect of interface-state charge. The gate insulator stack is found to contain a positive charge of 7.8\times10 11 cm-2 in units of the electronic charge, which clearly rules out the presence of 2-D hole gas and supports the normally- OFF operation of reported C-Si-O diamond devices. By using the high-low-frequency method, interface-state density at the Al2O3/SiO2/C-Si-O diamond interface was estimated to be in the range of 1.5\times10 11- 2\times10 12 eV-1cm-2 for interface-state energies of 0.4-0.82 eV above the valence band maximum of the diamond. These results form a basis for applying the silicon-terminated diamond to electronic devices.