Heavy phosphorus doping of diamond by hot-filament chemical vapor deposition

n-Type diamond is commonly fabricated with phosphorus doping and chemical vapor deposition (CVD). Phos-phorus atoms form a deep donor level of 0.57 eV below the bottom of the conduction band of diamond, making it difficult to reduce the electrical resistance of n-type diamond and also to form Ohmic contacts. Heavy doping is a promising technique to overcome these issues. In this study, we demonstrated heavy phosphorus doping for diamond with (111)-oriented surfaces by hot-filament CVD, which has the advantages of a large growth area and a simple apparatus configuration. The phosphorus concentration of the grown films was controllable in the range of 1018 to 1020 cm-3 by varying the ratio of phosphorus dopant, trimethylphosphine (PMe3), to methane in the gas phase. The electrical resistivity of the film with a phosphorus concentration of 1.2 x 1020 cm-3 was 42 omega cm at room temperature. This resistivity value is comparable to that of typical heavily phosphorus-doped n-type diamond films grown by microwave plasma-enhanced CVD. Our finding suggests that hot-filament CVD can be applied to the fabrication of low-resistive n-type diamond.