Synthesis and characterization of ZnO/ZnMgO multiple quantum wells by molecular beam epitaxy

Abstract

The growth of single and multiple (three) ZnO/ZnMgO quantum well samples on sapphire substrates, through a two-step temperature variation growth of ZnO buffer layers by molecular beam epitaxy (MBE), were investigated. For single quantum well (QW) growth, the thicker first ZnMgO barrier layer about 220 nm on the high-temperature growth ZnO (HT-ZnO) buffer layer, accumulated larger compressive stress, to achieve higher quality ZnO/ZnMgO QW growth. In the temperature-dependent photoluminescence (PL) results, the obvious S-shape variation of emission peak positions presented the stronger exciton confinement ability of QW in the higher magnesium concentrations of ZnMgO barrier layer growth. Compared to the control sample, the quantum confinement resulted in blueshift PL peaks of QW samples at low temperature. The multiple quantum well (MQWs) structure increased the exciton confinement ability to enhance the light emission efficiency of the sample. The three ZnO/ZnMgO MQWs structures were found clearly by high-resolution transmission electron microscopy.