A feasible, low temperature production of germanium nanowires: a photoelectrochemical study

A very simple, low-temperature CVD procedure using germane (GeH4) has been proposed to prepare deposits grown with germanium nanowires (GeNWs). Wide range of metal (Ag, Al, Au, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Pd, Pt, Sn, Ta, Ti, V, W, Yb, Zn and steel 246), oxide (fluorine-doped tin oxide - FTO) substrates as well as substrates from polytetrafluoroethylene (PTFE) and polydimethylsiloxane (PDMS) material were tested. Analytical techniques employed included scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Testing deposition temperatures were 220 and 280 °C, pressure was kept at 30 kPa and deposition time was 60 minutes. These deposition conditions are only representative; for a specific substrate, they can be tailored to particular applications for example to increase surface density and thickness of GeNWs. Selected copper substrates with the best GeNW coverage were studied in detail in the range 150 – 280 °C with step 10 °C and subsequently subjected to photoelectrochemical measurements. Using simulated solar light for illumination, the greatest photoelectrochemical performance was shown by a sample prepared at 220 °C, whose nanowires had an average diameter of 19.5 ± 2.3 nm. Planar samples prepared at 180 °C, as well as samples prepared at elevated temperatures of 280 °C and 330 °C, were surpassed in terms of the area-to-volume ratio and the superior free charge carrier separation due to a nanowire diameter that was less than the Bohr radius (24.3 nm).