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 x 10(18) cm-3 in the band conduction region up to 750K. 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.