A Study of Conformal GaAs on Si Layers by Micro-Raman and Spectral Imaging Cathodoluminescence
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1068-C02-06
A Study of Conformal GaAs on Si Layers by Micro-Raman and Spectral Imaging Cathodoluminescence Oscar Martínez1, Luis Felipe Sanz2, Juan Jiménez3, Bruno Gérard4, and Evelyn Gil-Lafon5 1 Física de la Materia Condensada, Universidad de Valladolid, Paseo de Belen 1, Edificio de I+D, Valladolid, 47011, Spain 2 Física de la Materia Condensada, Universidad de Valladolid, Paseo de Belen 1, Edificio I+D, Valladolid, 47011, Spain 3 Física Materia Condensada, Universidad de Valladolid, Paseo de Belen 1, Edificio de I+D, Valladolid, 47011, Spain 4 Corporate Research Laboratory, THALES, Orsay Cedex, 91404, France 5 LASMEA UMR CNRS 6602, Université Blaise Pascal, Les Cézeaux, Aubiére Cedes, 63177, France ABSTRACT Spectral imaging cathodoluminescence and micro-Raman spectroscopy studies of GaAs layers grown on Si substrates by the conformal method allow to reveal a great variety of physical features of the layers, such as the complete stress distribution, self-doping effects, or the incorporation of dopants. We present herein the characterization of GaAs conformal layers grown by hydride vapor phase epitaxy, where the main issues concerning the distribution of defects and stresses are revealed. Also, intentionally doped layers were analyzed, revealing the main aspects of the incorporation of dopant impurities during growth.
INTRODUCTION GaAs is a material of choice for optoelectronic applications due to its specific properties, with some important advantages over silicon, like the fact that it posses a direct band gap of 1.42 eV at room temperature [1]. In particular, this makes it the ideal semiconductor for the production of solar cells in terms of conversion efficiency [2]. It is also used for the fabrication of light emitting diodes and laser diodes [3]. However, it is rather expensive compared to Silicon, which prevents its introduction in some niches of volume production. GaAs based optoelectronic devices present a very low tolerance to the presence of dislocations. Epitaxial GaAs on Si substrates, that could benefit from drastic cost reduction, suffers form the large lattice mismatch (4%) and the large difference of thermal expansion coefficients (56%) between Si and GaAs [1], which results in dislocation densities, >106 cm-2, unacceptable for optoelectronic devices; e.g. the luminescence emission is dramatically quenched [4]. Therefore, one needs to explore alternative ways to prepare high quality GaAs epitaxial layers on Si. Among the alternatives to the direct GaAs/Si growth, the conformal growth, in which the GaAs layers grow laterally from GaAs seeds previously deposited on a Si substrate, have shown to produce a material with optical quality very improved, because the dislocation density is drastically reduced. A complete description of the growth method can be found elsewhere [5]. In this paper we investigated by means of spectral imaging (SI) cathodoluminescence (CL) in the scanning electron microscope (SEM) and micro-Raman spectroscopy (µ-R) the
optical properties of GaAs on Si layers grown by the c
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