Soft-solution route to ZnO nanowall array with low threshold power density

ZnO nanowall array (ZNWA) has been directionally grown on the buffer layer of ZnO nanoparticles dip-coated on Si-wafer under a soft solution process. Nanowalls on substrate are in most suitable shape and orientation not only as an optical trap but also as an optical waveguide due to their unique growth habit, V [ 01 1 ¯ 0 ] ⪢ V [ 0001 ] ≈ V [ 000 1 ¯ ] . Consequently, the stimulated emission at 384 nm through nanowalls is generated by the threshold power density of only 25 kW / cm 2 . Such UV lasing properties are superior to those of previously reported ZnO nanorod arrays. Moreover, there is no green (defect) emission due to the mild procedure to synthesize ZNWA.