The critical thickness was calculated, for capped and uncapped lattice-mismatched II-VI semiconductor epilayers, using both an old equilibrium theory and an improved theory. It was found that the observed values of the critical thickness were larger than the calculated values (as previously observed for GeSi and InGaAs strained layers). The discrepancy was attributed to the difficulty of nucleating dislocations. The strain relaxation was also calculated for layers which were thicker than the critical value. The observed strain relaxation in ZnSe layers on (100)GaAs exhibited good agreement with equilibrium theory. In other cases, the observed relaxation was sluggish and the residual strain was larger than the calculated value. It was noted that it had often been observed that the strain near to the surface of II-VI epilayers was small, and increased with increasing depth. An improved explanation for this observation was described. Excellent agreement existed between the predictions of this model and the observed strain distribution. A new model that was based upon continuum elasticity theory was used to explain strain oscillations during the initial stages of growth of highly mismatched layers, where the dislocations were usually distributed uniformly.

Critical Thickness and Strain Relaxation in Lattice-Mismatched II-VI Semiconductor Layers. K.Pinardi, U.Jain, S.C.Jain, H.E.Maes, R.Van Overstraeten, M.Willander: Journal of Applied Physics, 1998, 83[9], 4724-33