Optical and Structural Properties of Plasma-Treated ZnO Nanostructures

We studied the effect of plasma treatment on the structural and optical properties of ZnO nano-structures prepared by chemical bath deposition in an aqueous solution of Zn(NO3)(2) and hexamethylenetetramine. The room-temperature photoluminescence (PL) spectrum of the as-grown ZnO nanostructures exhibited two emission bands due to exciton emission and defect emission. After treating with hydrogen plasma, the treated ZnO nanostructures exhibited stronger exciton emission than the as-grown, untreated ZnO nanostructures in their respective cathodoluminescence and PL spectra. The low-temperature PL spectrum of the hydrogen plasma-treated ZnO nanostructures showed a strong exciton emission at 3.34 eV, attributing to the bound exciton and its longitudinal optical-phonon sidebands. The strong exciton emission is thought to be due to the combined effect of exciton emission enhancement by defect passivation and optical confinement resulting from nanostructure geometry.