Electronic transport properties of SiGe alloys and heterostructures grown by Sb assisted MBE

Abstract

Electronic transport properties have been measured in thin pseudomorphic SiGe alloys and heterostructures, grown by surfactant mediated epitaxy (SME), in order to investigate the unintentional doping effects caused by Sb, used as surfactant. In alloy films, we measured at 300 K, a Hall mobility ( μ H=20 cm 2 V −1 s −1) at least one order of magnitude lower than the undoped material ( μ H=100 cm 2 V −1 s −1), grown in similar conditions, but without surfactant. At low temperatures (40 K< T<75 K) we obtained μ H values of about 3.6×10 4 cm 2 V −1 s −1 for SME grown material and up to 5.5×10 4 cm 2 V −1 s −1, for undoped ones. Above 75 K, all the alloy samples showed a μ H decrease with the temperature steeply than the T −1.5 dependence. Moreover, in undoped materials we observed two distinct power law exponents. In SME (Si mGe n) p heterostructures we measured μ H values generally lower than 100 cm 2 V −1 s −1 at 300 K, due to the Sb high doping level. The strong doping effect caused by Sb in SME SiGe films suggests the use of different surfactant elements or alternative growth techniques in order to fabricate Si–Ge heterostructure based devices.