ELECTRONIC CONDUCTION IN RANDOM AL-GE FILMS

Electronic transport properties have been measured for 3500 Angstrom A l-Ge films with a random microstructure. The room temperature resistiv ity exhibits a sharp discontinuous jump at the metal-insulator transit ion, allowing for the direct determination of the critical metallic fr action, phi(c) = 8.8 vol% Al. A new procedure is described for extract ing values for the zero-temperature conductivity sigma(0) from the low -temperature conductivity data. When sigma(0) is extrapolated to zero as a function of Al content, the value obtained for the critical alumi nium fraction phi(c) is in excellent agreement with the value obtained from the room temperature data. The films exhibit two transition regi ons below 1.2 K as the Al content is decreased-a transition from the s uperconductivity state to the normal-metallic state, followed by a sec ond transition from the normal-metallic state to the insulating, varia ble-range-hopping state. Superconducting fluctuation data taken above 1.2 K were well described using the 2D Aslamazov-Larkin and Maki-Thomp son formulae; the 'resistive tails' below 1.2 K are also discussed.