Influence of oxidative and consequential reductive annealing on the photoluminescence intensity, decay time and morphology of ZnO single-crystal faces

Abstract Zinc oxide exhibits high electron mobility, wide 3.3eV band gap, ability to sustain large electric fields, relatively low electronic noise, and strong luminescence. These properties make ZnO invaluable for a broad range of applications. To optimize them, it is important to study the influence of annealing on ZnO properties under various conditions. In this work we compare the infrared Raman (IR Raman, 1064 nm laser excitation, 70-3500 cm 1 spectral range, 1cm 1 spectral resolution) and photoluminescence (PL, 360 nm UV LED excitation, 375-700 nm spectral range, 1 ns time resolution) optical spectra of as the received and annealed ZnO single crystals. The annealing has been done in oxidizing (air) and reducing (hydrogen) atmosphere at 350, 500 and 700°C. The Raman spectra consist of two characteristic peaks at 99 and 438 cm- 1 associated with the sublattice oscillations of Zn and O, respectively, and a broad PL band in the visible spectrum with mean time decay about 10 microseconds. The optical measurements are correlated with the topographical information obtained by atomic force microscopy (AFM). The result shows the ZnO single crystals can be enhanced in terms of PL intensity, decay time and optical scattering by annealing in the oxidizing and consequential reducing atmosphere. The trends are more profoundly on the O-face. Both treatments lead to greater surface roughness, particularly in the case of hydrogen atmospheres, but without any observable change in the IR Raman spectra.