Growth of detector grade CVD diamond films and microscopic interpretation of their efficiency and charge collection distance in the normal and pumpedstates

Microwave CVD diamond films with very high particle detection efficiency ha ve been obtained using a NIRIM-type reactor. The efficiency and charge coll ection distance (CCD) of nuclear particle detectors based on these films ha ve been systematically studied as a function both of the methane contents i n the growth gas mixture and of the film thickness. In particular, the effe cts of pre-irradiation with beta -particles (pumping) have been thoroughly studied. The detector response to 5.5 MeV alpha particles was (241) studied using a Am-241 source. Both efficiency and CCD behave in a markedly differ ent way in the as-grown and pumped states, the effect of pumping being stro ngly dependent on film thickness. These behaviors are analyzed, taking into account the polycrystalline nature of CVD diamond films, in the framework of a recently proposed model [Appl. Phys. Lett. 75 (1999) 3216] discussing the role of in-grain defects and grain boundaries in determining the charge collection spectra of diamond films in the normal and pumped states. Exper imental data are found to agree with what is expected from the model. The i nfluence of pumping on the detector resolution is also discussed. (C) 2001 Elsevier Science B.V. All rights reserved.