Nonpolar short-period ZnO/MgO superlattices: Radiative excitons analysis

Highlights: • Quasi-ternary ZnO/MgO alloys are grown by MBE as an alternative for random alloys. • The highest mean Mg concentration is reaching 72%. • Critical thickness of Mg layers for retaining wurtzite crystallinity is established. • Theoretical calculations confirm observed PL emission and deliver confirmation of ZnO QWs layers thicknesses. • CS-CL line scans revealed a ZnO D⁰X line blue shift in the SL, pointing to MgO thickness dependent biaxial strains build-up. The basic structural and detailed analysis of the optical properties of homoepitaxially grown ZnO/MgO superlattices (SLs) on a-oriented ZnO substrates, containing 30 periods of layers, was described. We found using Rutherford backscattering spectroscopy that the wurtzite coordination collapses in the SLs with 3 nm MgO thick barriers. This novel information allows taking this value as the limit for the maximum MgO barrier thickness in such structures. The observed luminescence and the performed calculations of excitonic transitions suggest that such a high energy barrier of MgO allows treating the ZnO layers in these SLs as separate, non-interacting quantum wells. Cross-sectional SEM-CL line scans revealed MgO layer thickness-dependent biaxial strains built up in the QWs structures.