Incorporation of arsenic in diamond grown by chemical vapor deposition

For the n-type doping of diamond, phosphorus is currently the only well-established substitutional donor. However, it is a relatively deep donor with an ionization energy of 0.6 eV. Theoretical studies show that other elements could behave as shallower donors in diamond. For instance, arsenic is predicted to have an ionization energy of 0.4 eV. In this work, we present a study on homoepitaxial diamond layers grown on (111) HPHT substrates by microwave plasma assisted chemical vapour deposition adding trimethylarsenic in the gaseous phase. A large set of growth conditions are investigated, starting with the ones classically employed for phosphorus doping. Some of the samples were also grown under a sequential gas flow that consists in a pulsed CH4 injection. Secondary ion mass spectrometry shows that arsenic is incorporated in the diamond layer. In addition, we show that, for a given [CH4]/[H-2] ratio, the arsenic incorporation ratio is larger with sequential growth than with continuous growth. However, the arsenic donor activity is not detected by cathodoluminescence spectroscopy. These results are discussed at the light of the diamond layer quality which is studied by Raman spectroscopy, Nomarski optical microscopy and electron channelling patterns. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.