Electrical conduction in homoepitaxial, boron-doped diamond films

Epitaxial, boron-doped diamond films were grown by hot-filament-assisted chemical vapour deposition (CVD) on (100) and (110) natural diamond substrates. Resistivity measurements for 10 K<T<500 K showed a clear transition from band to hopping conduction upon lowering of temperature. In the band conduction regime, the (100) films had higher conductivity than the (110) samples. The reverse was found in the hopping regime. This is explained by the difference in crystal growth mechanisms, leading to higher boron concentrations and lower carrier mobilities for (110) samples than for (100) oriented films. Hall effect measurements were performed for the most lightly doped (100) film at a boron level of 2.7*1018 cm-3 in the band conduction region up to 750 K. A mobility maximum of mu H=590 cm2 V-1 s-1 at 295 K was found, and the compensation ratio was determined to be smaller than 0.02. Some preliminary values for the Hall effective mass of valence band holes are given.