Influence of the growth parameters on the electrical properties of thin polycrystalline CVD diamond films

We report here results concerning significant improvement achieved in the growth of electronic grade chemically vapour deposited diamond films used for the fabrication of radiation detectors. We especially focused on the optimization of the carrier mobility and lifetime in thin (20 μm) undoped polycrystalline diamond films. Deposition temperature, methane concentration and microwave power density were systematically varied in order to establish deposition processes that provide adequate materials for alpha particle detection. Raman spectroscopy and scanning electron microscopy were used to probe the intrinsic quality of the films in term of solid state structure and purity. The electrical properties of the films were deduced from current-voltage characteristics and from the measurements of diamond detectors sensitivity to alpha particle irradiation (E = 5.5 MeV). Significant correlation was observed between the physico-chemical characteristics (crystallography quality by Raman line width, and purity by the qualitative ratio I_sp(2)/I_sp(3), nitrogen content) and electrical properties (resistivity, carrier mobility lifetime product) of sets of 20 μm thick films. In addition, at given growth parameters, the effect of diamond film thickness on their electrical properties was studied.