STRESS-RELAXATION IN LATERALLY SMALL STRAINED SEMICONDUCTOR EPILAYERS

The stress field in laterally small strained semiconductor epilayers has been studied by the finite element method. The reaction of the epilayer on the substrate and the bulging-out effect caused by shear forces in the side wall boundaries play an important role. Analytical approximate methods are shown to be deficient. The normal stresses relax faster than a simple exponential with height z and virtually complete relaxation occurs at a height h(eff)approximate to root ab/2 (where a and b are the width and length, respectively, of the parallellopipidial epilayer) which is in good agreement with recent experiments. An equivalent lattice spacing f(m) as a function of z/ root ab is defined and calculated.