Surface state density distribution of semiconducting diamond films measured from the Al/CaF2/i-diamond metal-insulator-semiconductor diodes and transistors

• DOI: 10.1063/1.365658
• Publication Date: 2002-07-26T13:52:43Z
• Authors: Young Yun; Tetsuro Maki; Takeshi Kobayashi
• Keywords: 0103 physical sciences; 01 natural sciences

Diamond metal-insulator-semiconductor diodes and field-effect transistors (MISFETs) have been prepared using CaF2 gate insulator and nondoped (in some cases, boron was doped) diamond homoepitaxial films. The resultant capacitance-voltage (C-V) curves and drain current-drain voltage (ID−VD) curves strongly depended on the amount of oxygen contamination of diamond surface. From analyses of C-V and ID−VD curves, it was found that the oxygen contamination induced the surface states with two distribution peaks locating very near the valence band edge and at the energy of ∼1 eV from the valence band edge. Although fluorination of oxygen-terminated diamond surface proceeded to a certain extent during CaF2 deposition at the elevated temperatures in vacuum, it still allowed surface state formation of about ∼1014/cm2 eV near the valence band edge due to uncompleted exchange of oxygen by fluorine atoms and easy penetration of residual oxygen in the chamber through the CaF2 insulator at elevated temperatures. Reduced-oxygen process by diamond surface passivation with hydrogen (hydrogenation) and room temperature deposition of CaF2 greatly improved the surface stability, and consequently, the surface state density near the valence band edge was reduced to ∼1012/cm2 eV. In this manner, the effective hole mobility of ∼10 cm2/V s was obtained from the diamond MISFET, which can be well compared with the surface Hall mobility of 35 cm2/V s.