  The rectified bulk photovoltaic effect (BPVE) in noncentrosymmetric
semiconductors, also called shift current, is considered promising for
optoelectronic devices, terahertz emission and possibly solar energy
harvesting. A clear understanding of the shift current mechanism and search for
materials with large shift current is, therefore, of immense interest. $ABC$
semiconductors LiZn$X$ ($X$ = N, P, As, and Sb) can be stabilized in cubic as
well as hexagonal morphologies lacking inversion symmetry$-$an ideal platform
to investigate the significant contributing factors to shift current, such as
the role of structure and chemical species. Using density-functional
calculations properly accounting for the electronic bandgaps, the shift current
conductivities in LiZn$X$ ($X$ = P, As, Sb) are found to be approximately an
order of magnitude larger than the well-known counterparts and peak close to
the maximum solar radiation intensity. Notably, hexagonal LiZnSb shows a peak
shift current conductivity of $\sim -75 ~\rm{\rm{\mu}}$A/V$^2$ and Glass
coefficient of $ -20$ $\times$ 10$^{-8}$ cm/V, comparable to the highest
predicted values in literature. Our comparative analysis reveals a quantitative
relationship between the shift current response and the electronic
polarization. These findings not only posit Li-Zn-based $ABC$ semiconductors as
viable material candidates for potential applications but also elucidates key
aspects of the structure-BPVE relationship.
