Spectroscopic investigation of homoepitaxial CVD diamond for detection applications

Three-layer structures consisting of intrinsic/B-doped homoepitaxial CVD diamond grown onto commercial HPHT Ib substrates have been studied by means of Raman spectroscopy and photoluminescence (PL). The intrinsic layers have been deposited, at fixed methane to hydrogen ratio (1%), by systematically changing the substrate temperature (620-820 °C). Raman measurements point out the excellent crystalline quality and phase purity of the samples. Moreover, flat PL spectra in a wide energy range (1.7 eV-2.7 eV) indicate also their great purity. As the free-exciton recombination can be used to further probe the quality of synthetic diamond, measurements of free-exciton emission at room temperature have been also performed. The excitation was produced by a 5 ns pulsed tunable laser irradiation. The results have been compared with the detection characteristics of simple alpha-particle detector prototypes based on the analyzed samples. A clear correlation between excitonic emission and detector sensitivity is demonstrated. On the basis of these results, low methane concentrations (approx. 1% CH4/H2) in the deposition gas mixture and intermediate substrate temperatures (approx. 720 °C-770 °C) have been identified as the best working conditions of our growth reactor.