Morphology and semiconducting properties of homoepitaxially grown phosphorus-doped (1 0 0) and (1 1 1) diamond films by microwave plasma-assisted chemical vapor deposition using triethylphosphine as a dopant source

Phosphorus-doped (1 0 0) and (1 1 1) diamond films were homoepitaxially formed on nondoped diamond films, which had been also formed homoepitaxially on type-Ib (1 0 0) and (1 1 1) diamond substrates, respectively, by microwave plasma-assisted chemical vapor deposition. Methane and triethylphosphine (TEP, P(C₂H₅)₃) were used as the carbon and dopant sources, respectively. When the P/C ratio in the gas phase was in the range of 10^-2-10^-1 and the methane concentration was 0.5%, smooth homoepitaxial (1 0 0) diamond films with a thickness of approximately 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 × 10^-2 contained sp² carbon. Phosphorus was found to be uniformly incorporated in the films, as evidenced by secondary ion mass spectroscopy, and the phosphorus concentration in the doped (1 0 0) diamond films was estimated to be (2-8) × 10¹⁸ 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 homoepitaxial (1 1 1) diamond film, which was formed at 1173 K using a gas-phase P/C ratio of 5 × 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 concentration and Hall mobility at 500 K were 3.8 × 10¹⁶ cm^-3 and 38 cm²/V s, respectively. Phosphorus was uniformly incorporated in the film at a concentration of 1 × 10²⁰ cm^-3.