MORPHOLOGY AND SEMICONDUCTING PROPERTIES OF HOMOEPITAXIALLY GROWN PHOSPHORUS-DOPED (100)DIAMOND AND (111)DIAMOND FILMS BY MICROWAVE PLASMA-ASSISTED CHEMICAL-VAPOR-DEPOSITION USING TRIETHYLPHOSPHINE AS A DOPANTSOURCE

Phosphorus-doped (1 0 0) and (1 1 1) diamond films were homoepitaxiall y formed on nondoped diamond films, which had been also formed homoepi taxially on type-Ib (1 0 0) and (1 1 1) diamond substrates, respective ly, by microwave plasma-assisted chemical vapor deposition. Methane an d triethylphosphine (TEP, P(C2H5)(3)) were used as the carbon and dopa nt sources, respectively. When the P/C ratio in the gas phase was in t he range of 10(-2)-10(-1) and the methane concentration was 0.5%, smoo th homoepitaxial (1 0 0) diamond films with a thickness of approximate ly 800 nm were obtained at 1123 K. Raman spectroscopy showed that the P-doped (1 0 0) diamond films formed with gas phase P/C ratios higher than 4 x 10(-2) contained sp(2) carbon. Phosphorus was found to be uni formly incorporated in the films, as evidenced by secondary ion mass s pectroscopy, and the phosphorus concentration in the doped (1 0 0) dia mond films was estimated to be (2-8) x 10(18) cm(-3). All P-doped (1 0 0) diamond films showed insufficient ohmic contacts for a Hall-effect determination, and no n-type conduction was confirmed. However, a hom oepitaxial (1 1 1) diamond film, which was formed at 1173 K using a ga s-phase P/C ratio of 5 x 10(-3) and a methane concentration of 0.1% on a nondoped homoepitaxial (1 1 1) diamond layer at 1123 K exhibited n- type conduction at temperatures higher than 485 K. The carrier concent ration and Hall mobility at 500 K were 3.8 x 10(16) cm(-3) and 38 cm(2 )/V s, respectively. Phosphorus was uniformly incorporated in the him at a concentration of 1 x 10(20) cm(-3). (C) 1998 Elsevier Science B.V . All rights reserved.