Shedding light on epitaxial SiGeSn alloys with Raman spectroscopy: local order and thermomechanical properties

Thanks to recent breakthroughs in their epitaxy compatible with industrial standard, (Si)GeSnalloys are now emerging as material platform for monolithic integration of next-generationelectronics, optoelectronics, thermoelectrics, and photonics. In order to support the rapidevolution of the (Si)GeSn material system, different advanced characterization methods have tobe developed to investigate its many interesting physical properties. This work provides anoverview of Raman spectroscopy investigation of binary GeSn and ternary SiGeSn alloys. Afterreviewing the fundamental principles of Raman spectroscopy, the typical features of (Si)GeSnalloy Raman spectra are introduced. These features are then attributed to vibrational modes ofatom pairs, high-order scattering, or disorder-induced scattering. The discussion also covers thedetails of polarization-resolved Raman spectroscopy applied specifically to the group-IV alloyscase, with a focus on probing the local atomic ordering. Different applications of the Ramanspectroscopy to the (Si)GeSn material system are covered. Initially, micro-Ramanmeasurements are complemented by ancillary techniques, such as x-ray diffraction. This allowsthe spatially resolved composition and strain of the investigated epitaxial alloys to bedetermined based on calibrated coefficients of vibrational mode shifts. Raman hyperspectralimaging, along with its integration with numerical simulations for strain mapping inmicrostructures and devices, is also presented.