Invited talk abstract

Diamond has been recognized as a promising semiconductor material for electronic applications due to its unmatched electronic properties. Natural diamond, high pressure high temperature (HPHT) diamonds and meanwhile also CVD-diamond are available with intrinsic and p-type properties where boron acts as deep acceptor about 370 meV above the valence band edge. n-type doping of diamond is, however, still elusive. In analogy to donors in silicon group V- (N, P, As) and VI-elements (S) in diamond are expected to act as donors if incorporated on substitutional sites. N-type doping by adding phosphine (PH3) to the CH4/H2 gas mixture in a microwave assisted plasma deposition has been demonstrated. Phosphorus is, however, a very deep donor with an ionization energy of 604 meV.

In this paper we show that homo-epitaxially grown CVD-diamond where H2S has been added to the CH4/H2-gas mixture during the growth also shows n-type conductivity. We apply Hall experiments, photoconductivity and photo-thermal ionization spectroscopy experiments to investigate the donor properties of sulfur. The results show that Sulfur is a double donor with ionization energies of the S (0/+)-transition (single ionization) of 370 meV and of the S (+/++)-transition (double ionization) of 480 meV. In this paper we show that homo-epitaxially grown CVD-diamond where H2S has been added to the CH4/H2-gas mixture during the growth also shows n-type conductivity. We apply Hall experiments, photoconductivity and photo-thermal ionization spectroscopy experiments to investigate the donor properties of sulfur. The results show that Sulfur is a double donor with ionization energies of the S (0/+)-transition (single ionization) of 370 meV and of the S (+/++)-transition (double ionization) of 480 meV. Both donor levels exhibit five detectable excited states that were studied from oscillatory photocurrent and photo-thermal ionization experiments. These data demonstrate that sulfur is an effective mass center in diamond. The LO-phonon energy is determined to be 161(+/-1) meV in agreement with indirect optical transitions at the conduction band minimum at k_min=(0,0,0.76). After annealing the sample at temperatures > 500 K the donor is fully compensated by deep defects, giving rise to an onset of optical absorption for photon energies hv >= 1 eV.