Bright-field transmission electron microscopy images, high-resolution transmission electron microscopy images, energy dispersive spectroscopy profiles, and high-resolution x-ray diffraction curves showed that a high density of ZnSe nanostructures with a small size was formed on the Cl-doped ZnSe thin films grown on GaAs substrates. The formation of the ZnSe nanostructures was attributed to the strain energy resulting from the existence of the compressive strain generated by the accumulation of Cl impurities on the surface of the ZnSe thin film and from the residual strain existing in the ZnSe thin film with a thin thickness. (C) 2007 American Institute of Physics.