Roughness enhanced surface defects and photoconductivity of acid etched ZnO nanowires

Wet chemical etching is utilized to enhance defect density by introducing surface roughness in ZnO NWs. Morphological investigations using SEM clearly show the surface roughness and the diameter/length decreases due to anisotropic etching of the NWs in 0.5-0.01M acid. Increased defect band intensity in PL measurements for etched samples indicates roughness induces defects at nanowire surface. Dark conductivity of NWs array film decreases after etching, this is due to creation of high depletion layer (higher concentration of surface adsorbed oxygen results in higher surface built- in potential) between NW grains. UV light irradiation results in three order enhanced conductivity for etched NWs array film, while only two order increase in conductivity has been measured in as-grown arrays. The enhancement in photosensitivity for etched nanowire is due to high surface defects created by the surface roughness. Higher surface defect states lead to slow photoresponse and high degree of persistency in photocurrent.