Systematic study of the normal and pumped state of high efficiency diamond particle detectors grown by chemical vapor deposition

The efficiency and charge collection distance (CCD) of nuclear particle detectors based on high quality diamond films grown by chemical vapor deposition (CVD) have been systematically studied as a function of the methane content in the growth gas mixture and for varying film thickness. The effects of preirradiation with beta particles (pumping) have been thoroughly studied. The results fully support a recently proposed model [Marinelli , Appl. Phys. Lett. 75, 3216 (1999)] discussing the role of in-grain defects and grain boundaries in determining the charge collection spectra of CVD diamond films both in the normal and in the pumped state. The model allows us to quantitatively explain the dependence of CCD and efficiency on film thickness, giving a microscopic picture of the effects of preirradiation with ionizing radiation in CVD diamond films. The highest average CCD obtained is 145 mum in a 160 mum thick detector (corresponding to about 50% average efficiency), while the maximum value (about 70% efficiency) is close to 370 mum. In addition, CCD is shown to be higher than film thickness and to monotonically increase with thickness, indicating margins for further improvements. (C) 2001 American Institute of Physics.