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

Abstract

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(C 2H 5) 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 sp 2 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)×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 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 3.8×10 16 cm −3 and 38 cm 2/V s, respectively. Phosphorus was uniformly incorporated in the film at a concentration of 1×10 20 cm −3.