A study was made of the effect of impurities upon the dislocation behavior in hetero-epitaxial ZnSe layers, on GaAs, which had been grown by means of photo-assisted organometallic vapor phase epitaxy. It was found that, in undoped ZnSe layers, the dislocation densities were similar to those in previous studies, where an inverse relationship between the layer thickness and the dislocation density had existed. The incorporation of Cl increased the dislocation density, relative to undoped layers of the same thickness. There was also a correlation between the normalized dislocation density and the concentration of incorporated Cl. The iso-electronic impurity, Cd, had a similar effect upon the dislocation density. The incorporation of Cd to a concentration of about 1020/cm3 increased the dislocation density by a factor of about 3 in comparison with undoped layers of equal thickness. It was also observed that doping with both Cd and Cl resulted in dislocation densities that were similar to those in undoped material. On the basis of the results, it was suggested that the controlling factor was the absolute value of the tetrahedral impurity misfit, rather than its sign, electronic activity, or the sub-lattice upon which it resided. A so-called impurity hardening model was proposed in order to explain the results. According to this model, the gliding of dislocations was inhibited, by the addition of impurities, due to local strain fields around the substitutional sites. The higher dislocation densities which were observed here after doping were concluded to be an indirect result of impurity hardening. In single crystals or pseudomorphic hetero-epitaxial layers, impurity hardening could inhibit the introduction of dislocations.

S.Kalisetty, M.Gokhale, K.Bao, J.E.Ayers, F.C.Jain: Applied Physics Letters, 1996, 68[12], 1693-5