Title: Fermi surface mediated enhancement of bulk photovoltaic effects in ZnGeP$_2$

Abstract: 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.