TRIMETHYLBORON DOPING OF CVD DIAMOND THIN-FILMS

Trimethylboron (B(CH3)3) has been used to obtain p-doped CVD diamond films in a microwave CVD reactor. Diamond films were grown from mixtures of methane, hydrogen and variable quantities of B(CH3)3 diluted in helium. We obtained samples with boron contents in the range 0.03-9 at.%. Raman analysis showed that samples with boron levels up to 0.2 at.% present an increase of film quality in terms of preserving diamond phase and decreasing the graphitic content. For higher boron concentrations the diamond Raman peak vanishes, and X-ray diffraction analysis shows an important expansion of the diamond crystalline network. Electrical measurements showed that, in samples with a boron content up to 0.2 at.%, the electrical conductivity increases by five orders of magnitude. For higher boron concentrations, the conductivity does not increase further. Using the temperature dependence of conductivity an activation energy of 0.1 eV and 0.17 eV was calculated in films with boron contents of 0.15 at.% and 0.03 at.% respectively. C-V measurements of the lowest doped sample, containing 0.03 at.% of boron, gave an acceptor density of 3 x 10(16) cm-3.