Temperature dependent spectroscopic study of the electronic structure of phosphorus in n-type CVD diamond films

In this work we used the quasi-steady-state photocurrent method and photothermal ionisation spectroscopy (PTIS) to study the electronic structure of the P-related level in n-type phosphorus doped CVD diamond. Previously, we reported the existence of two optically active defect levels, labelled X-P1 and X-P2, in the bandgap of these P-doped layers. X-P2 appeared to be only present in films showing high resistivity. Here we present a detailed PTIS and photocurrent study of the photoionisation cross-section, from liquid helium up to room temperature. At low temperatures, samples containing only the X-P1 defect show a phonon-induced oscillatory photoconductivity, giving information about the electronic structure of this defect. Additionally, with PTIS a sharp maximum was detected around 565 meV, originating from a thermal promotion of charge carriers from an excited state of the phosphorus-related level into the conduction band. We also discuss different models for the optical ionisation cross-section of the P-related level (e.g. shallow level, deep level). (C) 2000 Elsevier Science S.A. All rights reserved.