Influence of nitrogen incorporation on the electrical properties of MPCVD diamond films growth in CH4-CO2-N-2 and CH4-H-2-N-2 gas mixtures

Diamond films were elaborated in CH4-H-2-N-2 and CH4-CO2-N-2 gas mixtures i n a pulsed microwave plasma under the same working conditions, varying the percentage of nitrogen from 0.1 to 5.2%. Raman spectroscopy was used to pro be the quality of the film and the incorporation of nitrogen within diamond films was appreciated using cathodoluminescence (CL) spectroscopy. The int ensities of peaks due to nitrogen-vacancy pairs showed that the quantity of incorporated nitrogen increased with that of the nitrogen introduced in th e gas mixture. Arrhenius plots of the electrical conductivity showed that t he incorporation of low quantities of nitrogen in the diamond film led to a n increase in its resistivity. It can be speculated that small quantities o f incorporated nitrogen balance the natural p-doping of microwave plasma ch emical vapor deposition (MPCVD) diamond and, thus, enhance its insulating p roperties. Nevertheless, as higher quantities of nitrogen were incorporated , the resistivity of the diamond him decreased due to a possible n-doping. The doping hypothesis was confirmed by I-V measurements which exhibited a r ectifier behavior of the n-diamond/p-Si heterojunction structure. This beha vior was observed only in the case of a CO2-CH4 gas mixture, where a high c oncentration of nitrogen could be incorporated without affecting the contin uity of the film. (C) 2000 Elsevier Science S.A. All rights reserved.