Trapping-detrapping defects in single crystal diamond films grown by chemical vapor deposition

High-quality single-crystal diamond films were homoepitaxially grown by chemical vapor deposition onto low cost high-pressure high-temperature diamond substrates. The transport properties of the obtained samples were studied by photoresponse characterization. Fast ultraviolet (5 ns) laser pulses at 215 nm were used as a probe. The time evolution of the photoinduced current was observed to closely reproduce the laser pulse shape, thus indicating a time response lower than the adopted laser pulse duration. Very stable and reproducible response was measured, so that neither priming nor memory effects are observed. However, a minor slow component shows up in the charge-integrated sample response, whose temperature dependence was investigated in a $−25–+50°C$ range. A systematic speed up of this slow component of the sample signal is observed, indicating the presence of shallow centers producing trapping-detrapping effects. The experimental results are discussed in the framework of a trapping-detrapping model affecting the charge transport mechanism and an activation energy of $Ea=0.4eV$ was derived for the shallow trapping centers.