The results of studying the optical properties of nanoscale single crystals of MoS₂:Cl₂ and WS₂:Br₂ semiconductor compounds are presented. In microscopic images obtained at the wavelength of the second (400 nm), edge effects are detected, which consist in enhancement or reduction in the second-harmonic signal intensity. Unlike previously proposed interference mechanisms of edge effects, non-interference mechanisms are considered. The occurrence of edge effects is associated with either an increased Cl₂ and Br₂ halogen molecule concentration or with an electrically induced second harmonic caused by band bending at the edges of individual crystal layers.