The influence of technological parameters during the local Zn diffusion from the metalorganic source DEZn in the MOCVD reactor on the surface morphology of the InGaAs and InP layers was investigated. For a long-term process (more than 120 minutes) of local Zn diffusion into InP through the InGaAs surface layer, erosion of InGaAs surface was observed regardless of the material of the dielectric mask (SiO2, SiNx), the method of deposition of the dielectric mask (plasma chemical deposition or chemical vapor deposition) and method of etching of the dielectric mask (plasma chemical etching or liquid chemical etching). The effect of lateral Zn diffusion under the dielectric mask was formed on InGaAs/InP heterostructures has been studied. It was found that the depth of Zn diffusion in lateral direction into InGaAs is several times less than the depth of lateral Zn diffusion into InP layer. At the same time, a decrease in the thickness of the InGaAs surface layer leads to an increase in the depth of lateral diffusion of Zn under the mask due to the mechanism of vertical Zn diffusion from the InP:Zn region into the InGaAs surface layer.