Quaternary Phase Equilibria vs. Strain-Energy at the In. 53 Ga. 47 As/InP Interface
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QUATERNARY PHASE EQUILIBRIA VS. STRAIN-ENERGY AT THE In.53 Ga.47 As/InP INTERFACE
ALLAN E. SCHULTZ* AND Y. AUSTIN CHANG** *Honeywell/SSEC, 12001 Hwy. 55, Plymouth, MN 55441 **Y. Austin Chang, University of Wisconsin-Madison, Dept. of Materials Science and Engineering, 1509 University Av., Madison, WI 53706 ABSTRACT Extensive new data and modeling in the In-Ga-As system has allowed the authors to reexamine the phase equilibria between the melt and the epitaxial solid. A detailed thermodynamic model was constructed with the following improvements: (1) The solid-solid interaction parameters were based on InAs-GaAs miscibility gap data, and (2) liquid-bulk solid, as well as liquid-epitaxial solid, tie-lines were used. Comparison of tielines from epitaxial systems and bulk systems demonstrated that strain energy is not the dominant factor in equilibrium growth of epitaxial solid films of In -xGaxAs on any Ill-V binary substrate. Both the "latticepulling" effect and the "substrate-orientation" effect were shown to be caused by different quaternary equilibria at the Inl-xGaxAs/InP interface, and not by film-substrate strain. INTRODUCTION The liquid phase epitaxial growth of Ill-V films has resulted in two phenomena not observed in bulk growth, "substrate-orientation" and "lattice-pulling". The "substrate-orientation" effect reported by several authors [1,2,3,4,5] indicated that different orientations of the same substrate required different melts to grow the same solid. "Latticepulling", first claimed by Stringfellow [61 and later Joncour, et. al. [71, is the growth of a single, lattice-matched solid from a specific range of liquid compositions. Larche' and Cahn [81 derived equations that showed both effects were theoretically possible. Until the experimental work of the authors, however, liquid-bulk solid (i.e. non-epitaxial) tie-lines were not available for comparison with epitaxial films grown under LPE conditions. Also, the models for the bulk In-Ga-As system were not accurate enough to determine the effect of strain energy upon the phase equilibria. The model for both the solid and liquid phases was obtained by optimizing the data using a sub-regular solution model. Since the parameters for the solid solution are very sensitive to the critical point, the determination of the InAs-GaAs solid solution miscibility gap by the authors [9] made it possible to substantially increase the accuracy of the model. Tie-lines calculated from the model were compared with LPE tieMat. Res. Soc. Symp. Proc. Vol. 145. ©1989 Materials Research Society
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lines for Inl-xGaxAs/GaAs (x>0.85) to determine the effect of strain energy upon homoepitaxial deposition. Both the model, and the authors' bulk tie-line data, were used to analyze strain energy related effects for near lattice-matched In. 5 3 Ga. 4 7 As on InP substrates.
EXPERIMENTAL REVIEW InAs-GaAs miscibility gap determination The authors determined the phase boundaries of the miscibility gap in the InAs-GaAs solid solution by using a series of In/GaAs and Ga/InAs reaction co
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