Polarization-Insensitive Double Quantum Wells for Electro-Optical Applications

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9633780 Daniels-Race The goal of this project is to develop polarization-insensitive double quantum well (DQW) structures for applications in the modulation, detection, and amplification of optical signals. Specifically, we will investigate the growth and electron-hole interactions of tensile strained GaAs quantum wells sandwiched between InxA11-xAs barriers. With this configuration we are able to control the polarization characteristics of the optical response while maintaining compatibility with GaAs-based processing. The potential for the use of such structures in devices wherein polarization of the optical response is important has been demonstrated by our recent work in single quantum wells. In this 12 month project we will determine optimum MBE growth conditions which enhance the optical response at room temperature, as is required for device applicability. Using band-offset modeling in conjunction with optical techniques to examine structures of different barrier/well widths and strains, we will explore the DQW designs most suitable for further technological development. The primary methods of growth and characterization to be employed will be molecular beam epitaxy (MBE) and photoluminescence (PL) spectroscopy, respectively. These will be supported by electrical analysis techniques such as Hall and current-voltage measurements, X-ray diffraction, and both transmission and scanning electron microscopy. Optimal growth conditions will be examined by variation of MBE controlled (e.g.-substrate temperature, growth rate, V/III ratio, As overpressure) and structurally based (e.g.-well/barrier widths, strain, doping) parameters. As in our initial work, most of our studies will be of structures grown as GaAs substrates. However, we will also compare the optical characteristics of these structures to those of structures grown on ternary substrates, which provide lattice matching with the InA1As barrier layers. PL measurements, using temperature, excitation intensity and excitat ion wavelength, and polarization state variations, will be used to elucidate phenomena normally unobservable due to electron-hole transition selection rules for quantum wells. Our parallel goals with respect to the MBE and PL efforts will lay the necessary groundwork for development of practical devices based on these DQW's and similar structures. This is a collaborate research project between Theda Daniels-Race of Duke University and Laurie McNeil of the University of North Carolina-Chapel Hill. ***