Structure and optical properties of ZnO/ZnMgO multi-quantum wells grown on Si(111) substrates

A series of ZnO/Zn1−xMgxO multi-quantum wells (MQWs) were grown on Si(111) substrates by pulsed laser deposition (PLD), with different well widths and depths. Transmission electron microscopy (TEM) analysis revealed that all the samples exhibited a good periodic structure with clear interfaces. Moreover, temperature- dependent behavior of excitonic photoluminescence (PL) was investigated in order to investigate the mechanism of the carrier dynamics. In the temperature range studied, the luminescence was dominated by localized exciton (LE) emission, which was significantly blueshifted with respect to the ZnO single layer, due to the well-known quantum-size effect. The blueshift values increased with elevating Mg compositions in barrier layers or decreasing well thickness, being consistent with the calculated results. The relevant activation energies were deduced, varying in a range of 6.2 to 22 meV.