Photoluminescence from diameter-selected ZnO nanorod arrays

Arrays of ZnO nanorods with different, user-controlled, diameters were formed on Si substrates by 193 nm pulsed laser deposition in a low background pressure of oxygen. The effect of nanorod diameter on the photoluminescence exhibited by these arrays was investigated, as a function of incident ultraviolet (UV, 325 nm) laser intensity. Nanorods with large surface to volume ratios can exhibit high UV (∼380 nm) emission efficiencies, particularly when excited at higher incident intensities. Pre-illumination of such nanorods with 325 nm radiation serves to enhance the UV emission measured at lower incident intensities. These observations are rationalized in terms of photo-induced desorption of surface-bound oxygen, resulting in a quenching of the depletion layer at the ZnO surface. These findings serve to reinforce the potential of ZnO nanostructures for optoelectronic device applications.