High Resolution X-Ray Studies of Ga 1-x In x As Epilayers on GaAs Substrates
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HIGH RESOLUTION X-RAY STUDIES OF Ga 1 _-In.As EPILAYERS ON GaAs SUBSTRATES YUSHAN SHI* AND MARK SUTTON* *Center for the Physics of Materials and Department of Physics, McGill University, 3600 University Street, Montrial, Qudbec, Canada H3A 2T8
ABSTRACT By using the techniques of normal Bragg scattering and glancing incidence scattering, we have measured both the out-of-plane and in-plane structures of Ga 1 _-In.As epilayers grown on GaAs (001) face by MOVPE. The data presented in this paper were collected from two samples: a thick epilayer of 40,000A Ga 0 .8 4 In 0.16 As, and a thin epilayer of 500A Gao.sjIno. 19As, which are lattice-mismatched with the substrate by about 1.14% and 1.36% respectively according to the Vegard's law. The measured average lattice constants of the thick epilayer agree with the expectation both out-of-plane and in-plane and show nearly complete structural relaxation. An uniaxial in-plane modulation in the thick epilayer has been observed. The out-of-plane and in-plane data of the thin epilayer demonstrate a tetragonal distortion of the lattice, and the Poisson's ratio is calculated to be 0.36. The averaged in-plane lattice constant is still 0.18% larger than that of the substrate, which results in a complex structure at the epitaxial interface. An in-plane misalignment along one (110) axis in the thin epilayer has been observed.
1. INTRODUCTION The structure appearing during the initial stages of epitaxial growth is one of fundamental issues of heteroepitaxy and also one of the current topics of interest in condensed matter physics [1-3]. Theoretical studies were actually started in 1949 by Frank and van der Merwe who calculated the equilibrium ground state of epitaxial interfaces. They also predicted the existence of a critical thickness, below which the epilayer is strained to match the lattice of the substrate, and above which the dislocations are generated at the interface to release the accumulated elastic energy [4]. A large body of experimental work has been carried out since then to identify and characterize the misfit dislocation at the interface and test the critical thickness predications [5,6]. The discrepancy between theoretical calculation and experimental observation reveals our lack of understanding of heteroepitaxy as well as the great need of high resolution techniques for direct and comprehensive structural measurement. X-rays interact weakly with matter and the scattering pattern can be directly interpreted. Especially after the successful application of glancing incidence x-ray scattering (GIXS) for in-plane structural analysis [7], we are able to make a comprehensive and direct structural determination of epilayers and epitaxdal interfaces. In this paper, we will report a high resolution x-ray structural study of Ga 1 _-InAs epilayers grown on GaAs (001) face by metal-organic vapor phase epitaxy (MOVPE). The data presented here were collected from two samples: a thick epilayer of 40,000 AGao.s4 Ino.16As and a thin epilayer of 500 AGao.sjIn 0 .19As. According to th
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