Bulletin of the American Physical Society
2018 Annual Fall Meeting of the APS Ohio-Region Section
Volume 63, Number 15
Friday–Saturday, September 28–29, 2018; University of Toledo, Toledo, Ohio
Session A04: Condensed Matter Physics II |
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Chair: Scott Medling, The University of Toledo Room: SU 2592 |
Friday, September 28, 2018 1:30PM - 1:45PM |
A04.00001: Dynamical Stabilization in Delafossite Nitrides for Solar Energy Conversion Nathan Szymanski, Lauren Walters, Olle Hellman, Daniel Gall, Sanjay V Khare Delafossite structured ternary nitrides, ABN2, have been of recent experimental investigation for applications such as tandem solar and photoelectrochemical cells. We present a thorough computational investigation of the stability, electronic structure, and optical properties of nine compounds, where A = Cu, Ag, Au and B = Ta, Nb, V. Phonon density of states indicate all compounds to be dynamically unstable at low temperatures. Including finite-temperature anharmonic effects stabilizes all compounds at 300 K, with the exception of AgVN2. Crystal Orbital Hamiltonian Populations (COHP) provide insight into bonding and antibonding characters of A-N and B-N pairs. Instability at low temperatures can be attributed to strong A-N antibonding character. CuTaN2, CuNbN2, AgTaN2, and AgNbN2 are predicted to exhibit band gaps and large light absorption in the range of 1.0 to 1.7 eV, making these materials good candidates for solar-energy conversion applications. AuTaN2 and AuNbN2 have band gaps and absorption onsets near the ideal range for obtaining high solar-cell conversion efficiency, suggesting these compounds could become candidates as absorber materials in tandem solar cells or for band-gap engineering by alloying. |
Friday, September 28, 2018 1:45PM - 2:00PM |
A04.00002: Morphological transitions and stacking fault dislocation in Cu islands grown on strained Cu(100) Ehsan Sabbar, Indiras Khatri, Yunsic Shim, Jacques Amar A variety of experiments on submonolayer heteroepitaxial growth have demonstrated that the combined effects of strain and bonding can lead to shape transitions as well as dislocation formation. In order to separate out the effects of strain from “chemical” effects, we have used temperature-accelerated dynamics simulations to study a simple model system corresponding to the growth of Cu on a strained Cu(100) substrate. In the case of 2% compressive strain we find that - as previously found for Cu/Ni(100) growth [1] - multi-atom “pop-out” events are enhanced, leading to the formation of blobby islands with a mixture of open and closed step-edges. However, for much larger (4%) compressive strain, we find that island formation leads to the formation of dislocations. In contrast, dislocation formation does not occur in the absence of deposition. Finally, we find that - in good agreement with recent theoretical results [2] - a very large (8%) tensile strain leads to the formation of large anisotropic islands. The dependence of the barriers for monomer hopping and exchange on strain will also be discussed. [1] Y. Shim and J.G. Amar, Phys. Rev. Lett. 108, 076102 (2012). [2] J.G. Amar, Y. Shim, and R.T. Deck, Surf. Sci. 616, 120 (2013). |
Friday, September 28, 2018 2:00PM - 2:15PM |
A04.00003: Dielectric constants of α- Sn in the infrared region Jinsong Duan, Rigo Carrasco, Stephan Zollner, Stepanie Chastang, Gordon Grzybowski, Bruce Claflin, Arnold Kiefer α-Sn is a group-IV, zero-gap semiconductor with potential use in infrared |
Friday, September 28, 2018 2:15PM - 2:30PM |
A04.00004: Universal Connection of magnetic exchange and structural behavior under pressure in chromium spinels. Ilias Efthimiopoulos, Indiras Khatri, Terence T. Y. Liu, Sanjay V Khare, Pankaj Sarin, Vladimir Tsurkan, Alois Loidl, Zhang Dongzhou, Yuejian Wang We have conducted high-pressure x-ray diffraction studies on the MnCr2O4 and NiCr2O4 spinels at room temperature [1]. Both compounds undergo pressure-induced structural transitions into diverse tetragonal modifications. Based on these experimental observations and our ab initio calculations, we show that the Cr-oxide spinels with magnetic A2+ cations (A2+ = Mn, Fe, Co, Ni) follow a similar trend as their chalcogenide counterparts with nonmagnetic A2+ ions, i.e., the transition pressure is proportionally related with the magnitude of the Cr-Cr magnetic exchange interactions. Therefore, we reach the conclusion that the Cr-Cr magnetic exchange interactions alone suffice to account for the high-pressure behavior of these systems. Our results clearly depict the close relationship between the structural and magnetic degrees of freedom in Cr-bearing spinels. |
Friday, September 28, 2018 2:30PM - 2:45PM |
A04.00005: Interpretation of the effect of back surface etching on barrier height, carriers concentration and defects density of the CdTe solar cell devices Rasha A. Awni, Deng-Bing Li, Corey R. Grice, Zhaoning Song, Randy J. Ellingson, Michael J. Heben, Jian V. V. Li, Yanfa Yan Thin film CdS/CdTe photovoltaic devices have shown a potential interest by the researchers due to the low fabrication cost and high device stability. Developing an appropriate back contact for CdTe solar cells is crucial to achieve good device performance. In this work, we explore the impacts of hydrogen iodide acid etching on the back surface of CdTe solar cell devices to remove the back oxides and chlorides formed during CdCl2 treatment and form a Te-rich back surface. The back barrier height, carrier density and defect states are measured by temperature dependence of current-voltage (J-V-T), capacitance-voltage (C-V-T), admittance spectroscopy (AS) and impedance spectroscopy (IS) measurements. In C-V measurements, an appropriate AC modulation voltage and frequency will be selected, and DC bias voltage will be scanned. In AS and IS measurements, carriers or defects emission induces by applying small AC modulation voltage to be trapped and detrapped at certain frequencies and temperatures. An obvious increase in carrier concentration, suggesting an increased copper doping in the device. Additionally, the HI-treatment eliminates another defect level at 0.41 eV with respect to the valance band. All these improvements lead to better device performance of CdTe solar cells. |
Friday, September 28, 2018 2:45PM - 3:00PM |
A04.00006: A Simulation Tool for Ion Transport in Thin Film Semiconductors Anuja Parikh, Marco Nardone Cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) are the key materials used in the fabrication of thin-film photovoltaic devices. Migration of ions plays a significant role in the performance and degradation of such devices and is a topic of continuing research. This work focuses on diffusive transport in crystalline and polycrystalline solids with special attention to grain boundaries. The role of ion migration such as copper and phosphorous in CdTe and sodium in CIGS is reviewed using a general numerical simulation tool in this work. COMSOL Multiphysics® software is used to perform calculations using the finite element method. The output of this numerical modeling is validated against literature data. In addition, results of an empirical analysis will be presented for the case of sodium diffusion in polycrystalline CIGS. The extension of this work could be to enhance the capabilities of a device simulator by incorporating such ion transport mechanisms. |
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