Large bulk photovoltaic effect and Fermi surface mediated its enhancement with chemical potential in ZnGeP$_2$

Abstract

Bulk photovoltaic effect is a non-linear response in noncentrosymmetric materials that converts light into DC current. In this work, we investigate the optical linear and non-linear responses in a chalcopyrite semiconductor ZnGeP$_2$. We report large bulk photovoltaics namely shift and circular photogalvanic current conductivities which are 4.46 $\mu$A/V$^2$ and -5.49 $\mu$A/V$^2$ respectively with the incident photo energy around $\sim$ 5 eV at the chemical potential of E$_f$ = 0 eV which increase about 38\% and 81\% respectively at a chemical potential of E$_f$ = 1.52 eV. The systematic evolution of the bulk Fermi surface along with the high symmetry points in three dimensional Brillouin zone reveals the enhancement of bulk photovoltaics with the chemical potential in ZnGeP$_2$. To verify our findings, we further explore the distribution of bulk projected bands and surface Fermi surface distribution in the energy landscape using tight binding Hamiltonian within semi infinite slab geometry. This shows that the augmentation of bulk photovoltaics with the chemical potential is due to the surface Fermi surface states along the high symmetry $\Gamma-Z$ direction in Brillouin zone. Our thorough and detailed study not only provides a deeper understanding about the role of Fermi surface contribution to the bulk photovoltaic responses with chemical potential, but also suggests ZnGeP$_2$ as an ideal candidate for optoelectronics and bulk photovoltaics.