Electrically active sulfur-defect complexes in sulfur implanted diamond

Abstract

Single crystal type IIa 〈100〉 diamonds were implanted with sulfur, phosphorus, and argon ions under different implantation and annealing conditions. Shallow (sub-MeV) as well as deep (MeV) implantations into samples held at low (liquid nitrogen) ambient (room temperature) and high (400 °C) temperatures were employed. The implanted samples were subjected to postimplantation annealing up to 1000 °C. Following each processing step the samples were subjected to (i) Raman spectroscopy, in order to investigate the implantation related residual defects, and (ii) electrical (resistivity and sometimes Hall effect) measurements as function of temperature. The correlation between the results of these structural and electrical measurements and the comparison of results obtained under identical processing conditions for possible n-type dopant ion-implantations (S and P) and inert (Ar) ion-implantations, as controls, leads to the following conclusions: (a) Sulfur implanted samples always exhibit at least one order of magnitude higher conductivity than Ar control implanted samples. The activation energy associated with the S related conductivity is 0.32–0.37 eV whereas that of the Ar control is 0.5 to 0.6 eV. Hall effect shows, for selected cases, n-type conductivity with low carrier concentration and mobility. (b) Although the presence of some residual defects (mainly split interstitials) seems to accompany the appearance of the S related electrical activity, the level of residual damage in the S implanted samples is always less than that of the Ar control. (c) The electrical effects due to the implantation of S vanish upon annealing at temperatures in access of 800 °C. (d) No significant difference in the electrical properties between P and control Ar implantations are evident. It is concluded that a sulfur-defect related complex, which decomposes at T>800 °C, is responsible for the electrical effects in S implanted diamond. The presence of B contamination which has complicated the interpretation of experiments involving S doping during chemical vapor deposition diamond growth is excluded in the present work in which ion-implantation doping was employed.