Non-Equilibrium Carrier Dynamics in Bulk Chalcopyrite Crystals Studied with Time-Resolved Terahertz Spectroscopy

In this study, time-resolved terahertz spectroscopy (TRTS) is employed to investigate the ultrafast carrier dynamics and AC photoconductivity of cadmium germanium diphosphide (CdGeP₂), zinc germanium diphosphide (ZnGeP₂) and cadmium silicon diphosphide (CdSiP₂) chalcopyrite crystals. It is found that the terahertz (THz) transients decrease with increasing temperature due to the increase in thermally generated free carriers. Analysis of the differential THz transient reveals a two-component exponential relaxation. At elevated temperatures, complex AC photoconductivity decreases since conductive electron experiences increased scattering from the lattice phonons. Carrier density and scattering time are extracted by fitting complex AC photoconductivity with the Drude-Smith model. Carrier density decreases with pump-probe delay time since photoexcited carriers recombine or trapped. Carrier mobility decreases with increasing temperature due to increased scattering from phonons and thermally excited carriers at higher temperatures. This detailed understanding of photoexcited charge carrier dynamics and AC photoconductivity is crucial to potential applications of chalcopyrite crystals.