Optical characterization of GaAs/Si layers grown by the conformal method (confined lateral epitaxial growth)
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Martı´nez, M. Avella, and J. Jime´neza) Departamento de Fı´sica de la Materia Condensada, ETSII, Universidad de Valladolid, Valladolid, 47011, Spain
E. Gil-Lafon LASMEA UMR CNRS 6602, Universite´ Blaise Pascal, Les Ce´zeaux, 63177 Aubie´re Cedex, France
B. Ge´rard THALES, Corporate Research Laboratory, 91404 Orsay Cedex, France (Received 17 January 2002; accepted 11 March 2002)
Optical studies of conformal GaAs layers grown on silicon substrates were carried out by cathodoluminescence, photoluminescence imaging, and micro-Raman spectroscopy. These techniques revealed, in the conformal GaAs layers, local variations of the luminescence intensity with the shape of stripes both parallel and perpendicular to the GaAs seed, associated with local variations of tensile stress. The cathodoluminescence and micro-Raman spectra suggest that this distribution of tensile stress plays an important role in the formation of mid-gap states responsible for the variations of the luminescence intensity. The high luminescence emission of the conformal GaAs layers compared to the emission of the GaAs seed grown directly on the Si substrate is consistent with the high quality of the conformal layers.
I. INTRODUCTION
There is a big interest in the growth of high quality GaAs layers on a silicon substrate for the further integration of the high performance of GaAs with the large integration scale of Si. However, the attainment of defect free epilayers is subjected to some challenging problems because of the large lattice mismatch between Si and GaAs (4%) and the difference in the thermal expansion coefficients (55%). One must also deal with the difficulties of growing a polar semiconductor on a nonpolar one. Majority carrier devices with acceptable performance have been demonstrated1 but minority carrier devices, such as laser diodes, face the problem of the very high dislocation density (107–108 cm−2) of GaAs/Si epilayers. The defect density has to be reduced by several orders of magnitude (
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