Analysis of traps in high quality CVD diamond films through the temperature dependence of carrier dynamics

The analysis of the time behavior of pulses generated by CVD diamond films irradiated with a-particles has been recently shown to be a general and powerful tool to investigate trap properties in diamond films (M. Marinelli et al., Phys. Rev. B 64 (2001) 195205). We use here this technique to measure the activation energy of traps in CVD diamond films, through the analysis of the temperature dependence of the dynamics of carriers generated by a-particle irradiation. The samples used in this study are high quality films deposited in a microwave tubular reactor and show very narrow diamond Raman peaks (FWHM approximately 2.4 cm(-1)) and extremely low photoluminescence background. The time evolution of the response of alpha-particle detectors built from these films exhibit both a fast and a slow component. Quantitative analysis leads to the conclusion that only deep traps limit the electron mean free path before trapping, while for holes both deep and shallow centers must be taken into account, the latter becoming the limiting factor in the pumped state. The changes in the pulse shapes are analyzed when the film temperature T is varied from -40 to 20 degreesC. A systematic speed-up of the response is found with increasing temperature, confirming that the slow component is due to thermally activated detrapping from the relative shallow defects. The detrapping time constant tau(D) is connected to the activation energy E-D of the defects through the formula 1/tau(D) = s exp(- E-D/kT), where s is the attempt frequency. Plotting 1n(tau(D)) vs. 1/T allows to determine the activation energy of the shallow defects, which is found to be 0.35 eV. (C) 2003 Elsevier Science B.V. All rights reserved.