Electronic structure and spin-to-charge conversion in the chalcopyrite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>CdGeAs</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math>

Ternary semiconductors with chalcopyrite structure are of growing interest for electronic, energy-conversion, and spintronic applications. Using angle-resolved photoemission spectroscopy, we directly map the band structure of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>CdGeAs</a:mi> <a:mn>2</a:mn> </a:msub> </a:math> , the prototypical chalcopyrite described by a modified Kane model that predicts the coexistence of flat bands and highly dispersive linear states. The combined effect of tetragonal distortion and broken inversion symmetry reduces the band degeneracy, allowing us to resolve three distinct states at the top of the valence band, with band velocities comparable to those reported in Dirac semimetals. We further probe the spin-to-charge conversion properties of <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:msub> <b:mi>CdGeAs</b:mi> <b:mn>2</b:mn> </b:msub> </b:math> by optically injecting spin-polarized carriers and detecting the resulting inverse spin Hall effect (ISHE). The photon-energy dependence of the ISHE signal and theoretical calculations of the optically injected spin polarization allow us to identify the specific valence-to-conduction transitions responsible for net spin accumulation and to estimate the spin diffusion length. These results demonstrate that chalcopyrite semiconductors provide a versatile platform for optospintronics.