SURFACE-STATE DENSITY DISTRIBUTION OF SEMICONDUCTING DIAMOND FILMS MEASURED FROM THE AL CAF2/I-DIAMOND METAL-INSULATOR-SEMICONDUCTOR DIODESAND TRANSISTORS/

Diamond metal-insulator-semiconductor diodes and field-effect transist ors (MISFETs) have been prepared using CaF2 gate insulator and nondope d (in some cases, boron was doped) diamond homoepitaxial films. The re sultant capacitance-voltage (C-V) curves and drain current-drain volta ge (I-D-V-D) curves strongly depended on the amount of oxygen contamin ation of diamond surface. From analyses of C-V and I-D-V-D curves, it was found that the oxygen contamination induced the surface states wit h two distribution peaks locating very near the valence band edge and at the energy of similar to 1 eV from the valence band edge. Although fluorination of oxygen-terminated diamond surface proceeded to a certa in extent during CaF2 deposition at the elevated temperatures in vacuu m, it still allowed surface state formation of about similar to 10(14) /cm(2) eV near the valence band edge due to uncompleted exchange of ox ygen by fluorine atoms and easy penetration of residual oxygen in the chamber through the CaF2 insulator at elevated temperatures. Reduced-o xygen process by diamond surface passivation with hydrogen (hydrogenat ion) and room temperature deposition of CaF2 greatly improved the surf ace stability, and consequently, the surface state density near the va lence band edge was reduced to similar to 10(12)/cm(2) eV. In this man ner, the effective hole mobility of similar to 10 cm(2)/V s was obtain ed from the diamond MISFET, which can be well compared with the surfac e Hall mobility of 35 cm(2)/V s. (C) 1997 American Institute of Physic s.