THE INFLUENCE OF IMPURITIES ON THE DISLOCATION BEHAVIOR IN HETEROEPITAXIAL ZNSE ON GAAS

We have studied the influence of impurities on the dislocation behavio r in heteroepitaxial layers of ZnSe on GaAs, grown by photoassisted or ganometallic vapor phase epitaxy. In undoped ZnSe layers, the dislocat ion densities are similar to those obtained by [S. Akram, H. Eshani, a nd I. B. Bhat, J. Cryst. Growth 124, 628 (1992)] whose data show that there is an inverse relationship between layer thickness and dislocati on density. Incorporation of the electronically active impurity Cl inc reases the dislocation densities relative to undoped layers of the sam e thickness. Also, there is a correlation between the normalized dislo cation density and the concentration of incorporated Cl. The isoelectr onic impurity Cd has a similar effect on the dislocation density. Inco rporation of Cd to a concentration of similar to 10(20)/cm(3) increase s the dislocation density by a factor of about 3 compared to undoped l ayers of equal thickness. We also observed that doping of both Cd and Cl together resulted in low dislocation densities similar to the undop ed case. Based on our results, we believe that the controlling factor for this phenomenon is the absolute value of the tetrahedral misfit fo r the impurity, rather than its sign, or the electronic activity of th e impurity, or the sublattice on which the impurity resides. We propos e an ''impurity hardening'' model to explain these results. According to this model the glide of dislocations is inhibited by the addition o f impurities due to the local strain fields around the substitutional sites. The higher dislocation densities observed here with doping are an indirect result of impurity hardening. However, for single crystals or pseudomorphic heteroepitaxial layers, impurity hardening can inhib it the introduction of dislocations. (C) 1996 American Institute of Ph ysics.