Is sulfur a donor in diamond?

Homoepitaxial diamond layers grown by chemical-vapor deposition in the presence of ${\mathrm{H}}_{\mathrm{2}}\mathrm{S},$ which were published to exhibit n-type conductivity, are carefully analyzed both electrically and structurally. Hall-effect measurements as a function of temperature clearly show the samples to exhibit p-type conduction, with an activation energy, carrier concentrations, and mobilities which very much resemble those of B-doped p-type diamond. Secondary-ion-mass spectroscopy confirms that indeed the samples, previously claimed to be n type due to a donor state attributed to sulfur, contain enough unintentional boron to explain the observed p-type features.