Bulletin of the American Physical Society
2011 Annual Meeting of the Four Corners Section of the APS
Volume 56, Number 11
Friday–Saturday, October 21–22, 2011; Tuscon, Arizona
Session D3: Semiconductors |
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Chair: Charles Stafford, University of Arizona Room: UA Student Union Agave |
Friday, October 21, 2011 2:00PM - 2:12PM |
D3.00001: Electroluminescence Analysis of the Line Scribe Region in a CdTe Photovoltaic Module John Raguse Photovoltaic (PV) devices are a promising technology for future energy supplies. The high production rate of PV devices requires an in-line quality technique which is fast and provides information regarding the spatial performance of each unit. Measuring the electroluminescence (EL) signal is a quick technique used to map the spatial performance of a PV device. Cadmium Telluride (CdTe) modules have an array of repeating line scribes (P1, P2 and P3) which provide an electrical path to connect the cells in series, thus, creating a monolithically connected PV module. The region between the 3 line scribes is known as the ``inactive region'' due to the lack of carrier generation or recombination. Variations of the EL signal near the inactive region of a CdTe module were investigated. The increase in EL signal along the cell caused by larger voltage drops was observed. In addition, an unexpected second EL peak adjacent to the P3 line scribe was measured. It has been found that a second EL peak (adjacent to the P3 line scribe) is caused by a high density transparent conductive oxide region. [Preview Abstract] |
Friday, October 21, 2011 2:12PM - 2:24PM |
D3.00002: In-Depth Evaluation of CdTe Solar Cells Russell Geisthardt Thin-film polycrystalline CdTe solar cells have already had a significant research and commercial impact, but need to continue to improve in efficiency in order to contribute to the global energy supply. Device physics evaluation of these cells is crucial towards improving performance through better understanding of losses in efficiency. Standard evaluation techniques include current-density/voltage (J-V), quantum efficiency, and capacitance measurements. These measurements have been expanded to include variations in temperature and light intensity, which can be used to demonstrate non-ideal behavior of the current and voltage. Further graphical analysis of the J-V data has been done to determine diode parameters and parasitic losses. Data will be presented which illustrates the importance of these techniques by comparing non-ideal behavior with more ideal behavior. [Preview Abstract] |
Friday, October 21, 2011 2:24PM - 2:36PM |
D3.00003: Fractional quantum Hall effect and 5/2 state excitations in etch defined quantum point contacts Madhu Thalakulam, Wei Pan, K.W. Baldwin, L.N. Pfeiffer, K.W. West v=5/2 fractional quantum Hall (FQH) excitations are believed to obey non-Abelian statistics and posses topological properties. Most of the existing experimental studies on v=5/2 state has been conducted on macroscopic geometries where theoretically proposed studies to characterize the topological properties of the 5/2 state are usually based on confined geometries such as quantum point contacts (QPC). We have successfully fabricated QPCs on a high mobility GaAs/AlGaAs heterostructure using photolithography followed by etching and evaporation of Cr/Au depletion gates. Our samples show very stable FQH plateaus at v = 7/3, 5/2 and 8/3 filling fractions. Tunneling experiments are performed in these QPCs at various temperatures and also at various pinch-off voltages to characterize the effective charge and Coulomb interaction parameters of the quasiparticles. (Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.) [Preview Abstract] |
Friday, October 21, 2011 2:36PM - 2:48PM |
D3.00004: Temperature Dependence of SiO$_{2}$ Electron-Induced Luminescence Amberly Evans, Gregory Wilson, J.R. Dennison SiO$_{2}$ (fused quartz) is commonly used for optical instrumentation in space telescopes, including low temperature IR telescopes, where it can be exposed to electron fluxes from the space plasma environment. During recent charging tests of this dielectric material, a discernable glow was detected emanating from the surface of the SiO$_{2}$, indicating that the incident electron beam induced a luminescent effect. As the sample cooled from 300 K to 120 K, a change in the energy spectrum and intensity of the glow was observed between 250 nm to 1700 nm, implying that the luminescent property is temperature dependent. Luminescence results from transitions between extended conduction states and localized states below the mobility edge resulting from structural defects. Temperature dependent luminescence, including changes in relative peak intensities, results from changes in trap state population, accessible trap states, and transition states. Our observations are discussed in context with previous results of similar phenomenon and with simple models of disordered band theory. This work was supported by funds from NASA Goddard Space Flight Center. [Preview Abstract] |
Friday, October 21, 2011 2:48PM - 3:00PM |
D3.00005: Photoluminescence spectroscopy and transmission electron microscopy imaging of InGaAs quantum dot chains Tyler Park, Kenneth Clark, David Meyer, Andrew Perry, Scott Thalman, John Colton, Haeyeon Yang There are many potential uses of quantum dots, and specifically, quantum dot chains. We have obtained three InGaAs quantum dot chain samples that were grown using a modified Stranski-Krastanov technique. To study the quality and other aspects of these samples, we are using a number of techniques, among which are photoluminescence spectroscopy and transmission electron microscopy. Through photoluminescence spectroscopy, we hope to establish the quality of the quantum dots. With the transmission electron microscope, we hope to verify the size and spacing, identify the composition, and find out the segregation of the Indium in the dots. [Preview Abstract] |
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