TRIMETHYLBORON DOPING OF CVD DIAMOND THIN-FILMS

Trimethylboron (B(CH3)3) has been used to obtain p-doped CVD diamond f ilms in a microwave CVD reactor. Diamond films were grown from mixture s of methane, hydrogen and variable quantities of B(CH3)3 diluted in h elium. 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 ph ase and decreasing the graphitic content. For higher boron concentrati ons the diamond Raman peak vanishes, and X-ray diffraction analysis sh ows an important expansion of the diamond crystalline network. Electri cal measurements showed that, in samples with a boron content up to 0. 2 at.%, the electrical conductivity increases by five orders of magnit ude. For higher boron concentrations, the conductivity does not increa se further. Using the temperature dependence of conductivity an activa tion energy of 0.1 eV and 0.17 eV was calculated in films with boron c ontents of 0.15 at.% and 0.03 at.% respectively. C-V measurements of t he lowest doped sample, containing 0.03 at.% of boron, gave an accepto r density of 3 x 10(16) cm-3.