Raman and photoluminescence characterization of diamond films for radiation detectors

The structural quality of the diamond films (DF) deposited on a molybdenum (Mo) substrate seeded with micron-sizes diamond crystals and on unseeded one were characterized using micro-Raman (μ-RS) and photoluminescence (PL) spectroscopy. It was found that first-order μ-RS spectra of both films consist of three main peaks with the frequencies 1337 cm−1, 1393 cm−1 and 1569 cm−1. The mentioned peaks are attributed to the diamond vibration mode T2g in the center of the Brillouin zone, the vibration modes D(A1g) and G(E2g) of the disordered graphite structure and the crystalline one, respectively. The intensity of the diamond related line in the spectrum of DF on the seeded substrate is much smaller and the peak is wider (11.5 cm−1) relative to the natural diamond (2 cm−1); the peak is somewhat smaller and wider relative to the DF on the unseeded substrate (10 cm−1). Such features in the μ-RS spectra of both films indicate that the process of the substrate seeding with the diamond crystal seed leads to the synthesis of DF with a relatively small defect density and with a more homogeneous distribution of the residual strains. In the PL spectra, the lines caused by the recombination centers with the participation of the nitrogen impurity atoms are prevailing. The defects of the dominating type are the nitrogen-vacancy complexes [N-V]0 and [N-V]−. The intensities of the nitrogen complex related lines in the PL spectra of DF on the seeded substrate are smaller, which indicates smaller defects concentration than in the DF on the unseeded one. From the analysis of the μ-RS and PL data, we summarize that seeding of the substrate with diamond crystals leads to the improving of the crystalline perfection. However, the electrical measurements and the analysis of the performance of the detectors based on the DFs, show that DFs on the unseeded substrate have higher suitability for the detectors manufacturing.