Influence of growth kinetics on Sn incorporation in direct band gap Ge1xSnx nanowires

Ge1-xSnx alloys with substantial incorporation of Sn show promise as direct bandgap group IV semiconductors. This article reports the influence of growth kinetics on Sn inclusion in Ge1-xSnx alloy nanowires through manipulation of the growth constraints, i.e. temperature, precursor type and catalyst. Ge1-xSnx nanowire growth kinetics were manipulated in a vapour-liquid-solid (VLS) growth process by varying the growth temperature between 425 and 470 degrees C, using Au and Ag alloys as growth catalysts and different tin precursors such as allyltributytin, tertaethyltin and tetraallyltin. The profound impact of growth kinetics on the incorporation of Sn; from 7 to 9 at%; in Ge1-xSnx nanowires was clearly apparent, with the fastest growing nanowires (of comparable diameter) containing a higher amount of Sn. A kinetically dependent solute trapping process was assigned as the primary inclusion mechanism for Sn incorporation in the Ge1-xSnx nanowires. The participation of a kinetic dependent, continuous Sn incorporation process in the single-step VLS nanowire growth resulted in improved ordering of the Ge1-xSnx alloy lattice; as opposed to a randomly ordered alloy. The amount of Sn inclusion and the Sn impurity ordering in Ge1-xSnx nanowires has a profound effect on the quality of the light emission and on the directness of the band gap as confirmed by temperature dependent photoluminescence study and electron energy loss spectroscopy.