Electrical and structural properties of In-implanted Si_1-xGe_x alloys

We report on the effects of dopant concentration and substrate stoichiometry on the electrical and structural properties of In-implanted Si_1-xGe_x alloys. Correlating the fraction of electrically active In atoms from Hall Effect measurements with the In atomic environment determined by X-ray absorption spectroscopy, we observed the transition from electrically active, substitutional In at low In concentration to electrically inactive metallic In at high In concentration. The In solid-solubility limit has been quantified and was dependent on the Si_1-xGe_x alloy stoichiometry; the solid-solubility limit increased as the Ge fraction increased. This result was consistent with density functional theory calculations of two In atoms in a Si_1-xGe_x supercell that demonstrated that In-In pairing was energetically favorable for x 0.7 and energetically unfavorable for x 0.7. Transmission electron microscopy imaging further complemented the results described earlier with the In concentration and Si_1-xGe_x alloy stoichiometry dependencies readily visible. We have demonstrated that low resistivity values can be achieved with In implantation in Si_1-xGe_x alloys, and this combination of dopant and substrate represents an effective doping protocol.