The optical properties of high quality ZnO/ZnMgO quantum wells on Si(111) substrates

The ZnO/Zn0.85Mg0.15O multiple quantum wells (MQWs) were fabricated on Si(111) substrates by plasma-assisted molecular beam epitaxy (P-MBE) using ZnMgO as buffer layers. The RHEED images indicated that the MQWs were of high quality. The free exciton (FE) emission line originated from the well region and its phonon replicas (FE-1LO, FE-2LO and FE-3LO) were observed in the 86 K photoluminescence (PL) spectrum. Blueshift of the FE line in the MQW sample as compared to that in the ZnO bulk was found at temperatures as high as room temperature. Time-resolved PL study on the FE line showed a fast lifetime of 140 ps. The high quality of the MQW structure was revealed by the observation of the quantum-confinement-induced blueshift and shortened lifetime of the FE emission.