Electrical Properties of B-doped homoepitaxial diamond films grown from UHP gas sources

It is confirmed that a small amount of nitrogen incorporated into chemical vapor deposited diamond films dramatically affects their electrical properties. Nitrogen can be incorporated into diamond films through the leak of vacuum system and/or from the impurity in source gases. Because a nitrogen atom can be a deep donor in diamond crystal, the p-type semiconducting properties of boron doped diamond films can be degraded even by the small amount of nitrogen. The small amount of nitrogen in chemical vapor deposited diamond films was measured by cathodoluminescence spectroscopy. For the detection of nitrogen, the N-V center was intentionally induced by defect formation through ion beam irradiation and subsequent annealing. The luminescence intensity of the N-V center was decreased by reducing the leak of the vacuum system and by upgrading the purity of the source gases. Both the carrier density and the Hall mobility of the boron doped diamond films were successfully improved by the control of nitrogen contamination. Using extremely high pure CH4, H-2 and B2H6 in a tightly sealed vacuum system, the total amount of nitrogen impurity in the source gas was controlled to <80 ppm in the N/C atomic ratio resulting in a Hall mobility of 1600 cm(2)/Vs with a hole concentration of > 10(14) cm(-3) at the room temperature in a 10-ppm-boron doped homoepitaxial diamond film. (C) 1999 Elsevier Science S.A. All rights reserved.