Single crystalline and core–shell indium-catalyzed germanium nanowires—a systematicthermal CVD growth study

Abstract

Germanium nanowires were synthesized using thermal chemical vapor deposition (CVD)and indium as a catalyst. The process parameter space for successful growth wasstudied. By optimizing the growth temperature and gas pressure, high aspectratio germanium nanowires have been obtained. Scanning electron microscopyinvestigations indicate that the final diameter of the nanowires is strongly influencedby the growth temperature and the germane partial pressure. High resolutiontransmission electron microscopy reveals that nanowires grow either as high qualitysingle crystalline, or with a high quality single-crystalline core and a concentricamorphous shell. The occurrence of these two morphologies is found to only depend onthe wire diameter. Chemical analysis of the nanowire tip indicates the presenceof indium, validating its role as a catalyst. Raman spectroscopy measurementsreveal a higher incidence of core–shell structures for nanowires synthesized at30 Torr and indicate the presence of tensile strain. These results are importanttowards obtaining high quality germanium nanowires without the use of gold as acatalyst, which is known to degrade the wires’ electrical and optical properties.