The growth of cuprous oxide films for optical studies of excitons

Cuprous oxide (Cu₂O) possesses a rare crystal structure which leads to many interesting properties in this material. The existence of bound electron-hole pairs which interact repulsively and have a long lifetime in Cu₂O is one such property. Bound electron-hole pairs are known as excitons. It has been proposed that Cu₂O is a promising material for observing Bose-Einstein condensation (BEC) of excitons. Understanding this behavior in Cu₂O is of fundamental interest for explaining high temperature superconductivity. However, observation of the condensate has proven to be an elusive undertaking. The goal of this research is to develop single crystal-like, smooth, planar films of Cu₂O for optical studies of excitons. A major advantage of a thin film over bulk Cu₂O for observing BEC is spatial confinement of the excitons. However, the film must be highly crystalline and chemically pure in order to observe exciton signals with photo-luminescence (PL) spectroscopy.; Cu₂O films are chemical vapor-deposited (CVD) on MgO(110) single crystals. Attempting to improve Cu₂O film crystallinity results in enhancement of a three-dimensional island morphology. Data from x-ray diffraction spectroscopy (XDS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) demonstrate coherent epitaxial island growth on MgO(110). The isolated island morphology is explained by geometric stress relaxation at the free surface of the islands. This is the first observation of coherent islanding in an oxide film.; A Cu₂O film on MgO(110) is developed which is free of heteroepitaxial stress and single crystal-like. Evaporated Cu metal films on MgO(110) processed at high temperature and appropriate oxygen pressures form smooth, transparent, red films. XDS and TEM are used to show that the crystal structure of these Cu₂O films is distorted from bulk Cu₂O. A metastable phase of Cu₂O which is lattice-matched to the substrate is proposed. These films exhibit excitonic properties in both absorption and PL. It is hoped that further process improvements will lead to BEC observation in this material.