Low temperature photoconductivity detection of phosphorus in diamond

Abstract

Photocurrent measurements and the Constant Photocurrent Method (CPM) were used to carry out a spectroscopic study of epitaxial phosphorus-doped n-type CVD diamond films. Two optically active defect levels, X-P1 and X-P2, With photoionisation energy of 0.56 and 0.81 eV, respectively, found in previous work [1] are discussed in detail here. Comparison of CPM data with the activation energy of the carriers from Hall effect measurements suggest that the X-P1 defect can be attributed to the P-related donor level. X-P2 remains unidentified. Measurements carried out on a set of samples show that the X-P2 defect is only present in some samples showing high resistivity. To study the electronic structure of the X-P1 level, photocurrent measurements at low temperatures (liquid N-2 and liquid He) were done, revealing a phonon-induced oscillatory photoconductivity. Two sets of minima are observed which allow an estimation of the position of the first two excited states of phosphorus. Also a comparison is made with results from FTIR measurements.