Strain splitting of (formula presented) yellow orthoexciton of epitaxial orthorhombic (formula presented) films on MgO [110]

We investigated the optical properties of epitaxial orthorhomic cuprous oxide films grown on MgO [110]. Absorption measurements show clear excitonic peaks up to (formula presented) Photoluminescence at 2 K shows several sharp emission peaks in the vicinity of 610 nm associated with a splitting of various (formula presented) orthoexciton energy levels. The evolution of the peaks with temperature indicates that three peaks at higher energy are due to direct recombination of (formula presented) yellow orthoexcitons and three corresponding peaks at lower energy are their phonon replicas. The symmetry of each level is identified by the polarization properties of their photoluminescence emissions. The observed splitting of the energy levels is used to calculate the coherency strain based on an earlier-parametrized theory for the level splitting by Waters et al. based on the known symmetry of the electronic states. This predicted strain is compared with that determined by x-ray diffraction measurements of the measured lattice parameters.