High quality CVD diamond for detection applications: structural characterization

High quality synthetic diamonds have been grown on single-crystal silicon b y microwave plasma enhanced chemical vapour deposition, using a CH4-H-2 gas mixture at variable methane concentrations in the range 0.6-2.2%. Film sur face morphology and preferential orientation have been investigated by scan ning electron microscopy and X-ray diffraction. Raman spectroscopy and phot oluminescence (PL) have been utilized to monitor the crystalline quality an d to study the spatial distribution of defects in the deposited films, in v iew of their application as active materials for particle detectors. In par ticular, a detailed micro-Raman study shows that the diamond crystals on th e growth surface have intrinsic quality comparable with that of the best na tural diamonds, as evidenced by Raman peaks at 1332 cm(-1) narrower than 2. 4 cm(-1), by the complete absence of any non-diamond carbon feature at appr oximately 1500 cm(-1) and by a very weak luminescence background in the 100 -6500 cm(-1) spectral range. A broad PL band at approximately 2.05 eV, almo st completely absent at the growth surface, is detected moving towards the film-substrate interface. A worsening of the global quality of the films is found with increasing methane concentration in the gas mixture, as witness ed by the increased broadband PL in the films grown at higher methane conce ntrations. The excellent quality of the films was independently assessed th rough their high detection-performance. The alpha-particle spectra, measure d by using a 5.5 MeV Am-241 source, showed a decrease in the detection effi ciency with increasing methane concentration. This worsening in the detecti on performance is correlated with the lower global quality of the films gro wn at higher CH4 concentrations, clearly evidenced by the structural charac terization. (C) 2001 Elsevier Science B.V. All rights reserved.