We present a study of capping-barrier layer (CBL) effect on electro-optical properties of box- and spherical-shaped quantum dots as well as of the electronic transport of a QDs-array It is shown that increasing the CBL-width leads to a considerable enhancement in third-order optical nonlinear susceptibilities (14 times in the quadratic electro-optic effect, 31 times for ω = ω0/3 and 14 times for ω = ω0 in the third harmonic generation). The capping-barrier layer thus can be employed as a degree of freedom in engineering the electro-optical specifications of quantum-dot-based devices.