Electric evolution in sputter-deposited Sn_cSnSi_1-cSn alloy films

Sn_CSnSi_1-CSn alloy films (c_Sn: the chemical composition) have been prepared by rf sputter-deposition. X-ray diffraction measurement indicate that almost pure bct Sn and amorphous Si phases coexist for 0.28 ≤ c_Sn < 1.0. The electrical resistivity (p) measurement indicate that the alloy films are semiconducting above 10 K for cSn ≤ 0.47 and metallic for c_Sn ≥ 0.57, whereas they are superconducting below 4 K for c_Sn ≥ 0.38. When c_Sn is transformed to the volume fraction, v_Sn, the electrical conductivity, σ versus v_Sn plot shows clear inflection at around v_Sn = 0.41. This semiconductor to metal transition threshold (v_p ≅ 0.41) is much larger than 0.16 for the 3 dimensional site percolation theory, 0.21∼0.25 for the partially coalesced Sn-core/Si-shell cluster assemblies and 0.33 for the effective medium theory, but smaller than 0.5 for the granular materials in which metal grains are heavily coated by small insulator grain layers. Temperature dependence of p also reveals a transition from a simple energy gap type conduction to a thermally assisted electron tunneling type one with increasing vSn.