Emission of a Half-Rectangular Dislocation Loop from the Surface of a Compositionally Graded Epilayer
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TONG-YI ZHANG Department of Mechanical Engineering Hong Kong University of Science and Technology Clear Water Bay, Kowloon, Hong Kong ABSTRACT When a half-rectangular perfect or partial dislocation loop is emitted from the surface of a strained epilayer, the optimum dislocation shape occurs at a saddle point of the total energy profile as a function of the dislocation width and length. The activation energy and the optimum shape are calculated for either a compositionally graded or uniform epilayer. The results indicate that 1) dislocation emission is more difficult in a compositionally graded layer than in a compositionally uniform layer; and 2) the ratio of threading dislocation density to mismatch dislocation density is lower in a compositionally graded layer than in a compositionally uniform layer. Theoretical results agree with experimental observations [1,2]. INTRODUCTION Grading the buffer-layer composition can significantly reduce threading dislocation density. Fitzgerald et al. [1] observed that it is possible to obtain completely relaxed GexSil-x compositionally graded layers with 0. l
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