Continuous ZnO thin films have been grown at low temperature on -sapphire substrates in a radio-frequency magnetron-sputtering chamber employing a substoichiometric ZnO target with and without extra oxygen feeding. The effects of oxygen on the growth and band alignment of the heterostructures were investigated by using scanning-electron microscopy, x-ray diffraction, photoluminescence and transmittance/absorbance, ultraviolet-resonant Raman scattering, and x-ray photoelectron spectroscopy. Very remarkable changes of the structural and optical properties resulted from the introduction of oxygen: the surface hexahedral facets were diminished; the size of the surface islands and, hence, the compressive strains were reduced; ultraviolet transparency of the ZnO film was enhanced, together with an increased band gap due to the reduced intrinsic shallow-donor defects; and hence, the free-electron concentration. The offset in valence bands of the heterostructure was increased by at certain conditions. This is likely due to the increased Ga–O bonds at the interface by the incorporation of extra oxygen at the initial growth of ZnO.
Effects of oxygen on low-temperature growth and band alignment of heterostructures
H. F. Liu, G. X. Hu, H. Gong, K. Y. Zang, S. J. Chua; Effects of oxygen on low-temperature growth and band alignment of heterostructures. J. Vac. Sci. Technol. A 1 November 2008; 26 (6): 1462–1468. https://doi.org/10.1116/1.2990853
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