n-Type doping of diamond by sulfur and phosphorus

The n-type doping of diamond by sulfur and phosphorus has been investigated. Diamond thin films were grown epitaxially on (111) oriented synthetic type Ib crystals with phosphine added in the reactant gas ([P]/[C]=100-1500 ppm). Each grown sample was characterized by FTIR absorption and conductivity vs. temperature measurements. The infrared signature of neutral substitutional phosphorus appeared as two peaks located at 523 and 562 meV. Activation energy of the conductivity was approximately 490-550 meV above 400 K. All characterizations performed so far suggest a successful n-type doping by phosphorus. Sulfur-doped diamond thin films were grown on (100) oriented synthetic Ib crystals with H₂S ([S]/[C]=500-5000 ppm) added in the gas phase. Secondary electron microscopy, AFM and Raman scattering indicate a high quality homoepitaxy of the diamond film. The addition of H₂S induces a light green-gray or gray color of the doped film. The films are highly resistive after growth and oxidation of the surface, as usual undoped diamond. However, after light-illumination the electrical and photoelectrical properties change drastically. The results are interpreted in term of compensated semiconductor, taking into account contamination by boron atoms.