BORON-DOPED DIAMOND FILMS USING TRIMETHYLBORATE AS A DOPANT SOURCE IN METHANE CARBON-DIOXIDE GAS-MIXTURES

The effects of boron concentration in the gas phase on the morphological features and cathodoluminescence (CL) of polycrystalline diamond films were investigated. The diamond films were prepared on p-type Si(100) substrates by microwave plasma chemical vapour deposition. Trimethylborate vapour was introduced to the CH4-CO2 gas mixture as a dopant source. Secondary ion mass spectroscopy (SIMS), Raman and CL spectroscopy and scanning electron microscopy analysis were performed on the films. The depth profile of SIMS showed that boron was uniformly doped into the diamond film even at a depth of 6 mum. Boron was found to have a significant effect on both the morphology and cathodoluminescence of the deposited films. The surface morphology changed from well-defined facets to ball-like features with increasing gas phase dopant concentration. To obtain doped diamond films of good quality, it is necessary to lower the carbon concentration by decreasing the flow rate of CH4 during the deposition process. The cathodoluminescence of diamond films was investigated in the range 1.8-4.0 eV. The emission peak intensity of CL spectra at 2.3-2.4 eV was found to increase with increasing dopant concentration in the gas phase. The luminescence is explained by donor-acceptor pair recombination, where the acceptor is substitutional boron. This result indicates that the boron atoms can be successfully doped into substitutional sites of the diamond structure.