ABSTRACT
Abstract. ZnO grown on glass substrates by various thickness of MgO buffer layer has been investigated. All the layers are deposited by plasma-assisted molecular beam epitaxy. Without the MgO buffer layer, the surface cracks, due to the difference in the thermal expansion coefficients between ZnO and glass, are clearly observed. These cracks are drastically decreased with the MgO insertion. The photoluminescence emission intensity is also improved by increasing the buffer layer thickness until the optimum MgO thickness of 145 nm is reached. Few cracks start appearing with the reduction of the PL intensity when the buffer layer thickness is more than the optimised one. All of as-grown ZnO films without cracks exhibit n-type conductivity. 1
1. Introduction Recently, ZnO is receiving a great deal of attention as a promising material for the optoelectronic applications to the blue and ultraviolet regions because of its wide direct bandgap of 3.37 eV at room temperature and high exciton binding energy of 60 meV which opens the possibility of exploiting excitonic effects in room temperature devices. ZnO has been grown on various substrates such as ScAlMg04 [1], AI2 O3 [2,3], Si [4], CaF2 [5], and etc. However, to apply the ZnO optical devices into wide-area devices such as solar cells and TFTs, they are not as good as glass in terms of cost and size with the commercial availability. Therefore, the study of the ZnO growth on glass substrate is useful. The ZnO films grown on glass, however, suffer from high density of cracks because of the large mismatch in thermal expansion coefficients between ZnO and quartz glass.
