Exciton Localization of High-Quality ZnO/Mg_<i>x</i>Zn_1–<i>x</i>O Multiple Quantum Wells on Si (111) with a Y₂O₃ Buffer Layer

We report the structural and optical properties of ten-period ZnO/Mg_<i>x</i>Zn_1–<i>x</i>O multiple quantum wells (MQWs) prepared on the most widely used semiconductor material, Si. The introduction of a nanometer thick high-k Y₂O₃ transition layer between Si (111) substrate and a ZnO buffer layer significantly improves the structural perfection of the MQWs grown on top of it. The high structural quality of the ZnO/Mg_<i>x</i>Zn_1–<i>x</i>O MQWs is evidenced by the appearance of pronounced high order satellite peaks in X-ray crystal truncation rods; high resolution cross-sectional transmission electron microscopy images also confirmed the regularly arranged well and barrier layers. When the well width is less than ∼2.7 nm, the quantum-confined Stark effect in MQWs can be negligible. Not only the increasing exciton-binding energy but also reducing exciton–phonon coupling determined in temperature-dependent photoluminescence spectra indicate quantum-size effect. Our results demonstrate that ZnO/Mg_<i>x</i>Zn_1–<i>x</i>O MQWs integrated on Si have great potential in UV optoelectronic device applications