CAPACITANCE-VOLTAGE MEASUREMENTS ON METAL-SIO2-DIAMOND STRUCTURES FABRICATED WITH (100)-ORIENTED AND (111)-ORIENTED SUBSTRATES

Metal-SiO2-diamond structures were fabricated using (100)- or (111)-oriented substrates of type IIb natural diamond, which is a p-type semiconductor. The SiO2-diamond interface was electrically characterized by measuring the capacitance between the metal electrode and the diamond substrate as a function of bias voltage. Capacitance-voltage (C-V) characteristics were measured for various SiO2 thickness and substrate temperature, with and without exposure to ultraviolet light. When biased into depletion, the metal-SiO2-diamond structures showed no indication of minority-carrier electrons accumulating at the SiO2-diamond interface. This is believed to be due to the low electron generation rate in the diamond and the small barrier for electrons to enter the SiO2 from the diamond conduction band. For (100)-oriented substrates, the capacitance varied substantially with temperature near accumulation, but showed no significant change in depletion. Exposure of (100)-oriented substrates to ultraviolet light, which generates conduction-band electrons in diamond, resulted in the accumulation of electrons at the SiO2-diamond interface, which affected the C-V measurements. On the other hand, this light had no substantial effect on the (111)-oriented substrates, because of the absence of a barrier for electrons to enter the SiO2. From the C-V measurements, the conduction band of diamond was determined to be 2.3 eV below and 0.7 eV above vacuum level for (100)- and (111)-oriented substrates, respectively. Metal-SiO2-diamond structures on (100)-oriented substrates appear to be acceptable for depletion-mode metal-oxide-semiconductor field-effect transistors (FET's), while (11)-oriented substrates may be used as robust cold cathodes.