Browsing by Autor "G. Marcano"

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    Electrical properties of CuGaTe2
    (Wiley, 1983) S. M. Wasim; G. Marcano; G. Sánchez Pérez
    A systematic study is made on the effects of annealing CuGaTe2 single crystals in vacuum, under reduced pressure, and in the presence of Cd and Zn. From the variation of hole concentration with temperature, the acceptor state ionization energy is found to lie between 18 and 37 meV. This energy state is associated with Ga vacancy. There is some indication that Zn acts as donor in this compound. The mobility data are explained by taking into account the scattering of the charge carriers by ionized and neutral impurities, acoustic-mode phonon, and space charge effects. The valence-band deformation potential is found to be 4.32 eV. Une étude systematique a été faite sur les effets de récuit des cristaux simples de CuGaTe2 dans le vide, sous pression réduite et en presence des élements Cd et Zn. La variation de la concentration des trous avec la temperature a été établie et l'energie d'ionisation des états de l'accepteur a éte trouvée comprise entre 18 et 37 meV. Cet état d'energie est associé avec la vacance de l'élement Ga. C'est une indication que le Zn a joué le rǒle de donneur dans ce composé. Les données relatives à la mobilité ont éte obtenués et expliquées en prenant compte les différents mechanismes de dispersion des porteurs de charges y compris les impuretés ionisées et neutres, les phonons de mode acoustique et les effets d'espace de charge. Le potentiel de deformation de la bande de valence trouvé est égal à 4,32 eV.
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    PREPARATION, CRYSTAL STRUCTURE, THERMAL ANALYSIS, SCANNING ELECTRON MICROSCOPY AND OPTICAL BAND-GAPS OF Cu 2 GeTe 4 AND Cu 2 SnTe 4 ALLOYS ( PREPARACION, ESTRUCTURA CRISTALINA, ANALISIS TERMICO, MICROSCOPIA ELECTRONICA DE BARRIDO Y BRECHA OPTICA DE ENERGIA DE LAS ALEACIONES Cu 2 GeTe 4 Y Cu 2 SnTe 4 )
    (2015) P. Grima; Ricardo Peña; Luis Nieves; G. Marcano; Miguel Quintero; Ekadink Moreno; Jacilynn A. Brant; Jennifer A. Aitken
    Polycrystalline samples (weight ~ 1g) of Cu 2 GeTe 4 and Cu 2 SnTe 4 alloys were prepared by the usual melt and anneal method and the products characterized by X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM) and Optical Diffuse Reflectance UV/VIS/NIR Spectroscopy techniques. It was found that: a) Cu 2 GeTe 4 and Cu 2 SnTe 4 crystallize in an orthorhombic structure (s.g. Imm2; N o 44) with lattice parameters a=5.9281(4) A, b=4.2211(6) A, c=12.645(5) A and a=6.0375(6) A, b= 4.2706 (3) A, c=12.844(1) A, respectively; b) both alloys show two thermal transitions: 762 and 636K upon heating and; 700 and 578K upon cooling for Cu 2 GeTe 4 ; 702 and 636K upon heating and; 650 and 590K upon cooling for Cu 2 SnTe 4 ; c) both alloys present large deviations of stoichiometry for the cations Cu (~35%), Ge (7.2%) and Sn (26.4%) and minor deviation within the experimental error, for the anion Te; and, d) the measured optical band gaps were 0.63 and 0.53 eV for Cu 2 SnTe 4 and Cu 2 GeTe 4 , respectively. Se prepararon muestras policristalinas (peso ~ 1 g) de las aleaciones Cu 2 GeTe 4 y Cu 2 SnTe 4 por el metodo de fusion y recocido y los productos caracterizados por las tecnicas de Difraccion de Rayos X (DRX ) , Analisis Termico Diferencial (ATD), Microscopia Electronica de Barrido (MEB) y espectroscopia de reflectancia optica difusa UV / VIS / CIR. Se encontro que : a) Cu 2 GeTe 4 y Cu 2 SnTe 4 cristalizan en una estructura ortorrombica ( g.e. Imm2; N o 44 ) con parametros de red a = 5,9281 (4) A , b = 4.2211 (6) A , c = 12.645 (5) A y a = 6.0375 (6) A , b = 4,2706 (3) A , c = 12.844 (1) A , respectivamente ; b) ambas aleaciones muestran dos transiciones termicas : 762 y 636K al calentar y ; 700 y 578K tras el enfriamiento para Cu 2 GeTe 4 ; 702 y 636K al calentar y ; 650 y 590K tras el enfriamiento para Cu 2 SnTe 4 ; c) ambas aleaciones presentan importantes desviaciones estequiometricas en sus cationes: Cu (~35%), Ge (7.2%) and Sn (26.4%) y menor que el error experimental para el anion Te; y d) las brechas opticas de energia medidas fueron 0.63 y 0.53 eV para Cu 2 SnTe 4 y Cu 2 GeTe 4 , respectivamente.