Stress Effects on nP Yellow Excitons in Cu2O Thin Films Recrystallized Epitaxially in a Sample Gap between Paired MgO Substrates

We investigated the stress effects on nP yellow excitons in Cu2O thin films recrystallized epitaxially in a sample gap between paired MgO substrates. In such samples, it is expected that a two-dimensional compressive stress acts on Cu2O because of the slightly larger lattice constant of Cu2O than of MgO. To clarify such stress effects, we measured the X-ray diffraction and nP absorption transitions of the yellow excitonic system and analyzed the strain and stress effects. Although the detected lattice strain and the energy shift of the yellow excitonic band gap are smaller than the values expected from the lattice mismatch at the heterointerface, this can be explained self-consistently by considering strain and stress relaxations in Cu2O thin films with departing from the MgO heterointerface. Consequently, we can find that shallow trapping potentials for the yellow excitons are formed in the similar to 1.3-mu m-thick region interfaced with the MgO substrates.