Optimization of the Process Conditions for the Growth of Large, Optical Quality Crystals of Cupric Oxide (NU ANL LDRD Subcontract)

High quality single crystals are of critical importance for the development of photonic technologies, which are used in many applications including spectroscopic techniques used in chemistry and physics research as well as in data storage applications. To keep pace in the areas of physics, chemistry, and biology where such lasers are required, it is first important to make such new materials, and second to have state-of-the-art crystal growth facilities capable of producing high quality crystals. This project will focus on the optimization of the process conditions for the growth of large, optical quality crystals of cupric oxide. We have begun collaboration with Nicholas Laszlo Frazer and Professor John Ketterson in the Northwestern University Department of Physics to use our crystal growth capabilities to grow large, pure crystals of cuprous oxide, Cu2O. Cu2O has a third harmonic generation capability, and provides us an opportunity to improve our crystal growth technique, and investigate how growth parameters effect crystal quality. Additionally, cuprous oxide experiences an extremely long exciton lifetime, up to 13 microseconds [A. Mysyrowicz et. al., A. Phys. Rev. Lett. 1979, 43, 1123], which makes it an ideal material for studying exciton behavior. An exciton-mediated photo-voltaic effect can be used to measure excitons with high spatial resolution. To use this method, a large, high quality single crystal is required. A large sample is needed in order to deposit electrodes on the sample. The sample must be of high quality in order to prevent the excitons from scattering before reaching the electrodes. The exciton travels to the surface of the sample, which is coated with copper and gold electrodes. The electron falls into the copper electrode, and an accumulation of charge in the copper electrode creates an electric field which draws the hole into the gold electrode. The current between the two electrodes is measured. A number of factors effect exciton path length, including impurities and defects. In order to maximize the exciton path length, these factors must be minimized. Finally, a large single crystal can be oriented and cut along any desired face, allowing the electrodes to be deposited along any plane. Orientation is important since it determines optical selection rules.