Optical Absorption of Large Band-Gap Sb x Bi 1-x I 3 Alloys
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Optical Absorption of Large Band-Gap SbxBi1-xI3 Alloys C. Persson†, R. Ahuja, J. Souza de Almeida and B. Johansson Condensed Matter Theory Group, Department of Physics, Uppsala University, Box 530, SE-75121 Uppsala, Sweden C. Y. An and F.A. Ferreira Instituto Nacional de Pesquisas Espaciais, INPE/LAS - C.P.515, 12201-970 São José dos Campos, SP, Brazil N. Souza Dantas Departamento de Ciências Exatas, Universidade Estadual de Feira de Santana ,Br 116, Km 03 Campus Universitário , 44031-460 Feira de Santana, Ba, Brazil I. Pepe and A. Ferreira da Silva* Instituto de Física, Laboratório de Propriedades Ópticas, Universidade Federal da Bahia, Campus Universitário de Ondina 40210-340 Salvador, Ba, Brazil ABSTRACT The optical properties of SbBiI3 alloys have been investigated experimentally by absorption measurements and theoretically by a full-potential augmented plane wave (FPLAPW) method within the generalized gradient approximation. The fundamental band-gap energy of these alloys changes from BiI3- to SbI3-like with increasing percentage of Sb content. The calculated band-gap energies as well as the optical absorption were found to be in a very good qualitatively agreement with the experimental results. We present calculated density-of-states as well as the dielectric functions for evaluation of future experiments. Introduction SbxBi1-xI3 alloys have very large band-gap energies and are therefore very promising materials for development as room temperature gamma-ray detectors and non-linear applications. But so far very little is actually known about the physical properties of BiI3 and SbI3 and even less about SbxBi1-xI3 [1,2]. These materials have hexagonal structures, similar to PbI2, which has large applicability as room temperature detectors [3]. The fundamental band-gap energies of these alloys change from BiI3- to SbI3-like, i.e., from about 2.3 to 2.0eV. In this work, we have investigated the optical properties of SbBiI3 alloys, both experimentally and theoretically. A transmission spectroscopy technique has been used for the measurements of the optical band-gap energies. The calculatiosn of the absorption, density-of-states (DOS) and dielectric functions were performed by the fullpotential linearized augmented plane wave (FPLAPW) method [4], choosing the exchange-correlation potential of Perdew, Burke, and Ernzerhof [5].
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Experimental details The experimental transmission spectroscopy apparatus consists of a halogen lamp used as the light source for the measurement. The polychromatic beam is diffracted by plane diffraction gratings attached to a step motor. The beam can be varied from 850 to 360nm corresponding to phonon energies from 1.46 to 3.44 eV; a set of lens and collimator produces a monochromatic light focused onto the sample. A first order bandpass filter has been used to avoid an eventual second order contamination of the monochromatic light, which in the intrinsic resolution, obtained by the calibration process, is 1.2 nm or 0.2%. The angular spread of the beam at the sample locati
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