GROWTH AND CHARACTERIZATION OF CVD DIAMOND WIRES FOR X-RAY-DETECTION

In order to gain insight into the mechanism of diamond growth on metal lic wires (50-500 mu m diameter), we have investigated the deposition process in a hot filament chemical vapour deposition (HFCVD) reactor. A two-dimensional model of our HFCVD reactor was developed in order to interpret the experimental data which indicate an evident influence o f the substrate wire diameter on the gas species concentration and oil the diamond growth rate. The theoretical model indicates a reduction of the growth rate as the substrate diameter increases due to the redu ction of hydrogen and the active radicals concentrations at the substr ate as its growth area increases. In view of a possible application of . such samples as X-ray detectors, we investigated their electrical pr operties by analysing the current/voltage characteristic in, a metal/d iamond/metal geometry at different temperatures. The activation energy of the conductivity is found to be dependent on the applied electric field. The experimental data support a Poole-Frenkel conduction with o verlapping centres. Finally the response of our diamond wires to X-ray radiation flux was investigated. A sensitivity of about 5 x 10(-6) As Gy(-1) was measured under a 100 keV Bremsstrahlung X-ray flux and the photocurrent is almost linear with respect to X-ray tube current. (C) 1997 Elsevier Science S.A.