Synthesis of Germanium Nanowires in Supercritical Fluid Reactors

Abstract

Relatively high intrinsic carrier concentration (2.4 X 1013 cm-3) and carrier mobility (3900 cm2/V∙s for electron and 1900 cm2/V∙s for hole respectively) of germanium (Ge) make germanium nanowires (Ge NWs) an attractive candidate as a charge transport channel in various devices. Ge NWs can be synthesized by injecting Ge atoms in gold seed particles at a temperature above the eutectic point of Ge and Au (361 ℃). A large-scale synthesis of Ge NWs is possible by using dense fluid as a reaction media. Here, we used a supercritical fluid reactor, and successfully synthesized Ge NWs, with diameter ranging from 15 nm to 100 nm and length of several µm. In order to attain supercritical fluid, anhydrous hexane was heated and pressurized above its critical point The optimum reaction temperature ranged from 425 ℃ to 450 ℃, while the pressure did not cause substantial changes in final product as long as it is above the critical point. Below 400 ℃, amorphous Ge particles were synthesized. Depending on reaction conditions, Ge NWs exhibited widely different morphologies. In this research, we discuss the effect of various reaction conditions such as temperature, and Au:Ge ratio on the nanowires.