Growth and properties of CVD diamond films grown under H2S addition

The influence of H2S on the CVD diamond growth, the sulfur incorporation and the electronic properties of sulfur containing homoepitaxial diamond films were studied. Laser reflection interferometry (LRI) in combination with mass spectroscopy (MS) showed that H2S modifies the gas phase chemistry by reducing the concentration of CHx species. As a consequence thereof, at high deposition temperatures the growth rate decreased. At lower substrate temperatures, the observed increase in the growth rate after sulfur addition indicates that these gas phase effects are overcompensated by processes at the growing diamond surface. The incorporation coefficient of sulfur into the definitely boron free diamond films was very low (less than 10(-6)). Incorporation seems to be enhanced by a reduction of the substrate temperature, by the presence of Si and, most effectively, by addition of CO2. For 0.5% CO2 in the gas mixture a maximum S concentration of 480 ppm (9 X 10(19)/cm(3)) corresponding to an incorporation coefficient of 6 X 10(-4) was attained. Even for the highest H2S concentrations (nearly I 1%) the deposited diamond films preserve their excellent quality as judged from mu-Raman measurements. The electrical properties were not changed by the S incorporation. The electrical conductivity is thermally activated with typically 1.4-1.5 eV independent from the S concentration in the films. No values below 1.0 eV have been measured which argues against doping. (C) 2002 Elsevier Science B.V. All rights reserved.