Vapor-liquid-solid growth of SnO2 nanowires utilizing alternate source supply and their photoluminescence properties

Vapor-liquid-solid (VLS) growth of tin dioxide (SnO2) nanowires (NWs) on the c-plane sapphire substrate coated with the Au film (5-30 nm in thickness) was performed by atmospheric-pressure CVD utilizing alternate source supply (ASS) of tin (Sn) and water (H2O). X-ray diffraction measurements and scanning electron microscope (SEM) observations revealed the successful growth of SnO2 NWs by the ASS technique. The ASS technique was found to be effective for suppressing the enhancement of the NWs average diameter caused by the increase in growth temperature (Tg). In the cycle number range from 300 to 800, the NWs average diameter was almost independent of cycle number, indicating that the radial growth due to vapor-solid (VS) growth was suppressed. PL spectra of the NWs were dominated by a broad orange band (OB) emission (~ 1.9 eV) associated with oxygen vacancy (VO) and/or interstitial tin atom (Sni). Mirror reflection symmetry between the PL and PLE spectra with a very large Stokes shift indicated a strong coupling between the deep-level defect and phonons in the optical transition process. The enhancement of the OB emission with increasing Tg is probably due to the increase in the density of the structural defects composed of VO and/or Sni.