Magneto-transport properties of As-implanted highly oriented pyrolytic graphite

We report on magneto-transport experiments in a high-quality sample of highly-oriented pyrolytic graphite (HOPG). Magneto-resistance and Hall resistivity measurements were carried out in magnetic inductions up to B=9T applied parallel to the c-axis at fixed temperatures between T=2 K and T=12 K. The sample was submitted to three subsequent irradiations with As ions. The implanted As contents were 2.5, 5 and 10 at% at the maximum of the distribution profile. Experiments were performed after each implantation stage. Shubnikov-de Haas (SdH) oscillations were observed in both the magneto-resistance and Hall-effect measurements. Analyses of these results with fast Fourier transform (FFT) lead to fundamental frequencies and effective masses for electrons and holes that are independent of the implantation fluences. The Hall resistivity at low temperatures shows a sign reversal as a function of the field in all implanted states. We interpret the obtained results with basis on a qualitative model that supposes the existence of an extrinsic hole density associated to the defect structure of our sample. We conclude that the As implantation does not produce a semiconductor-type doping in our HOPG sample. Instead, an increase in the extrinsic hole density is likely to occur as a consequence of disorder induced by implantation.