Characterization of boron-doped diamond films using (CH 4-CO 2) gas mixtures with B(OCH 3) 3 as a dopant source by MPCVD

Abstract

Boron-doped diamond films were fabricated on p-type and n-type Si(100) substrates by microwave plasma chemical vapour deposition. Tri-methylborate vapour was introduced to the CH 4-CO 2 gas mixtures 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 μ. Boron was found to have a significant effect on both the morphology and the 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 CH 4 during the depostion 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 boron atoms can be successfully doped into substitutional sites of the diamond structure.