Resolving transient conductivity dynamics in phosphorus-implanted GeSn alloys using optical pump-terahertz probe spectroscopy

GeSn alloys have garnered significant interest for electronic and optoelectronic applications over the past decade, primarily because of their monolithic compatibility with complementary metal–oxide–semiconductor fabrication platforms, tunable band structure, extended optical absorption into the short-wave infrared range, and excellent charge-transport properties. Recently, ion-implanted GeSn has been explored for the fabrication of photoconductive terahertz (THz) devices as a competitive alternative to low-temperature-grown III–V compound semiconductors. Since their ultrafast photoconductivity response governs the THz performance of such devices, this work provides a comprehensive characterization of the transient optoelectronic properties of ion-implanted GeSn alloys under different implantation doses and energies. In particular, optical pump–THz probe measurements were performed to assess the photoconductivity dynamics more accurately, while the Drude–Smith model was employed to extract the transient optoelectronic parameters of the samples under ultrafast excitation. Complementary characterization techniques, such as x-ray diffraction (XRD), photoluminescence (PL), and scanning electron microscopy (SEM), were also used to gain deeper insight into the properties of the ion-implanted GeSn samples. The results show that GeSn treated with moderate ion-implantation dose and energy exhibits an optimized balance between short carrier lifetime, good crystallinity, and high mobility, highlighting the importance of defect engineering for tailoring the transient optoelectronic properties of GeSn for ultra-broadband THz sensors. These findings are expected to support the development of next-generation GeSn-based functional devices.