CRITICAL THICKNESS AND STRAIN RELAXATION IN LATTICE-MISMATCHED II-VI SEMICONDUCTOR LAYERS

Critical thickness h(c) has been calculated for capped and uncapped la ttice mismatched II-VI semiconductor epilayers. Both the old equilibri um theory and the improved theory have been used. The calculated value s are compared with the experimental data on epilayers of several II-V I semiconductors and alloys. The observed values of h, are larger than the calculated values, a result similar to that observed with GeSi an d InGaAs strained layers. The discrepancy is attributed to the difficu lty in nucleating the dislocations. Strain relaxation in layers with t hickness h>h(c) is also calculated. Observed strain relaxation in ZnSe layers grown on (100) GaAs shows good agreement with the equilibrium theory. In other cases, the observed relaxation is sluggish and the re sidual strain is larger than the calculated value. Many authors have o bserved that strain near the surface of the II-VI epilayers is small a nd increases as the depth increases. We describe an improved model to explain this observation. The agreement between the prediction of our model and the observed strain distribution is excellent. A new model b ased on continuum elasticity theory is described to explain strain osc illations during the initial stages of growth of highly mismatched lay ers. In highly mismatched layers, the dislocations are distributed uni formly. A model to interpret this observation is suggested. (C) 1998 A merican Institute of Physics.