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 (similar to 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.