PLAN-VIEW DIFFRACTION CONTRAST IMAGING OF SURFACE-RELAXATION EFFECTS FROM STRAINED-LAYER SUPERLATTICES

Two-beam electron diffraction contrast imaging techniques have been used to study surface-stress-relaxation effects from Ge(x)Si1-x/Si strained-layer superlattices (SLS) imaged in plan-view. Strong, "anomalous" black/white strain-field contrast is observed due to lattice plane bending where coherently strained layers emerge at the free surface of a back-thinned foil. In addition, differential thinning-induced steps can give rise to superimposed fringe-contrast effects in very thin foil regions; the latter effect is shown to make a much smaller contribution to the total diffraction contrast. The results presented here indicate the importance of understanding stress-relaxation effects in plan-view electron diffraction where strained layers emerge at a free surface.