Diamondlike carbon films on semiconductors for insulated-gate technology

MIS structures are fabricated on p-type InP, GaAs, and Si substrated by direct ionization of 25-percent CH4 in Ar and ion-beam deposition of 70-nm-thick diamondlike films, followed by application of Al gate electrodes and ohmic contacts. The films are found to have bandgap 0.9-1.1 eV, resistivity 8.1 Mohm cm, breakdown field strength 1 MV/cm, and density 1.8 g/cu cm, to be thermally stable up to 400 C, and to undergo rapid decomposition above 450 C. The electrical properties of the MIS structures are significantly improved by sputter cleaning the substrates with a 1-keV 2-mA/sq cm Ar beam for 2 min at 300 microtorr prior to C-film deposition. The resulting structures have fixed insulator charge number densities 4 x 10 to the 12th/sq cm (InP), 7.5 x 10 to the 12th/sq cm (GaAs), and 9 x 10 to the 11th/sq cm (Si) and interface state densities (5, 200, and 0.5) x 10 to the 12th/ sq cm eV, respectively. It is suggested that the low optical bandgap and resistivity of the C films and the high insulator-charge and interface-state densities make them unstable as gate dielectrics for microelectronics.