Monolithic infrared silicon photonics: The rise of (Si)GeSn semiconductors

(Si)GeSn semiconductors are finally coming of age after a long gestation period. The demonstration of device-quality epi-layers andquantum-engineered heterostructures has meant that tunable all-group IV Si-integrated infrared photonics is now a real possibility.Notwithstanding the recent exciting developments in (Si)GeSn materials and devices, this family of semiconductors is still facing serious limitationsthat need to be addressed to enable reliable and scalable applications. The main outstanding challenges include the difficulty to growhigh-crystalline quality layers and heterostructures at the desired content and lattice strain, preserve the material integrity during growth andthroughout device processing steps, and control doping and defect density. Other challenges are related to the lack of optimized devicedesigns and predictive theoretical models to evaluate and simulate the fundamental properties and performance of (Si)GeSn layers and heterostructures.This Perspective highlights key strategies to circumvent these hurdles and hopefully bring this material system to maturity to createfar-reaching opportunities for Si-compatible infrared photodetectors, sensors, and emitters for applications in free-space communication,infrared harvesting, biological and chemical sensing, and thermal imaging