Electrical properties of boron-doped diamond films synthesized by MPCVD on an iridium substrate

Boron-doped diamond films were synthesized on an iridium substrate by microwave plasma-assisted chemical vapor deposition, using trimethylboron as the dopant source. The Ir substrate was bias-treated by the constant-current mode to permit the formation of oriented diamond nuclei. In order to isolate the B-doped diamond layer electrically from the Ir substrate, the non-doped diamond particles that were formed were grown in the 〈1 0 0〉 and then 〈1 1 1〉 directions and finally, a B-doped layer was synthesized to give a B/C ratio of 100-400 ppm. Surface morphology, Hall mobility and hole concentration were investigated for the resulting B-doped diamond films. The Hall mobility was closely related to the surface morphology of the diamond films. After optimizing the synthesis conditions, a Hall mobility of 340 cm^-2 V^-1 s^-1 and hole concentration of 2 × 10¹⁰ at 250 K was obtained for a heteroepitaxial B-doped diamond film synthesized at a B/C ratio of 200 ppm. These values are smaller than previously reported values for homoepitaxial B-doped diamond film.