Controlling heterojunction abruptness in VLS-grown semiconductor nanowires via in situ catalyst alloying

For advanced device applications, increasing the compositional abruptness of axial heterostructured and modulation doped nanowires is critical for optimizing performance. For nanowires grown from metal catalysts, the transition region width is dictated by the solute solubility within the catalyst. For example, as a result of the relatively high solubility of Si and Ge in liquid Au for vapor-liquid-solid (VLS) grown nanowires, the transition region width between an axial Si-Ge heterojunction is typically on the order of the nanowire diameter. When the solute solubility in the catalyst is lowered, the heterojunction width can be made sharper. Here we show for the first time the systematic increase in interface sharpness between axial Ge-Si heterojunction nanowires grown by the VLS growth method using a Au-Ga alloy catalyst. Through in situ tailoring of the catalyst composition using trimethylgallium, the Ge-Si heterojunction width is systematically controlled by tuning the semiconductor solubility within a metal Au-Ga alloy catalyst. The present approach of alloying to control solute solubilities in the liquid catalyst may be extended to increasing the sharpness of axial dopant profiles, for example, in Si-Ge pn-heterojunction nanowires which is important for such applications as nanowire tunnel field effect transistors or in Si pn-junction nanowires.