Co-Doping of Diamond with Boron and Sulfur

Characterization of diamond co-doped with boron and sulfur is reported. SIMS analysis shows that the sulfur is concentrated in the near surface region, although increased concentrations of sulfur above background levels appear in the bulk diamond as well. Hall effect and thermoelectric power measurements indicate that the conductivity is n-type in the surface region and can be either n- or p-type in the bulk, depending on the degree of compensation with boron. The co-doped samples are not stable at elevated temperatures and there is an irreversible loss of conductivity when heated above 400 K in air. Electrochemical polarization of the n-type diamond showed blocking at anodic potentials up to +5 V versus the saturated calomel electrode. Two types of p/n junctions using the n-type boron/sulfur co-doped diamond were made: one using boron-doped diamond as the p-type side and the other using the p-type surface conductivity induced by hydrogen termination. The turn-on voltage in both junctions was approximately 0.5 V, which suggests that the Fermi level in the n-type diamond is low in the band gap. The n-type conductivity likely arises from an impurity band. The nature of the centers giving rise to the conductivity is not known.