  Bulk photovoltaic effect is a non-linear response in noncentrosymmetric
materials that converts light to a DC current. In this work, we investigate the
optical linear and non-linear responses of the chalcopyrite semiconductor
ZnGeP$_2$. We report the enhancement of bulk photovoltaics namely shift and
circular photogalvanic (CPG) current conductivities due to intrinsic
contribution of Fermi surface along the high symmetry $\Gamma-Z$ direction. We
observe that the magnification of shift and CPG current conductivities around
the incident photon energy $\sim 5$ eV are about 38\% and 81\% respectively in
ZnGeP$_2$ due to shifting of Fermi level to 1.52 eV. To further verify our
findings, we explore distribution of bulk Fermi surface states in both three
dimensional Brillouin zone and surface Fermi surface distribution in the
projected energy landscape using semi infinite slab geometry. Our study not
only provides a deeper understanding of the roles of Fermi surface contribution
on the bulk photovoltaic responses, but also suggests the ZnGeP$_2$ is an ideal
candidate for optoelectronics.
