Ignatii Zaitsev

Germanium–tin (GeSn) microdisks have emerged as promising structures for CMOS‐compatible light sources. Their emission properties depend on the composition of the GeSn alloy, strain, and temperature. In particular, optical and electronic properties are sensitive to the distribution of mechanical strain introduced during the growth process and patterning steps. Understanding how mechanical constraints and structural configurations influence the optical mode confinement and band structure is crucial for optimizing GeSn‐based laser devices. In this work, we present a comprehensive computational investigation into the mechanical deformation and optical behavior of GeSn microdisks fabricated on silicon substrates combining photoelasticity, analysis of optical modes and band structure calculations.

Thanks to recent breakthroughs in their epitaxy compatible with industrial standard, (Si)GeSn alloys are now emerging as material platform for monolithic integration of next-generation electronics, optoelectronics, thermoelectrics, and photonics. In order to support the rapid evolution of the (Si)GeSn material system, different advanced characterization methods have to be developed to investigate its many interesting physical properties. This work provides an overview of Raman spectroscopy investigation of binary GeSn and ternary SiGeSn alloys. After reviewing the fundamental principles of Raman spectroscopy, the typical features of (Si)GeSn alloy Raman spectra are introduced. These features are then attributed to vibrational modes of atom pairs, high-order scattering, or disorder-induced scattering. The discussion also covers the details of polarization-resolved Raman spectroscopy applied specifically to the group-IV alloys case, with a focus on probing the local atomic ordering. Different applications of the Raman spectroscopy to the (Si)GeSn material system are covered. Initially, micro-Raman measurements are complemented by ancillary techniques, such as x-ray diffraction. This allows the spatially resolved composition and strain of the investigated epitaxial alloys to be determined based on calibrated coefficients of vibrational mode shifts. Raman hyperspectral imaging, along with its integration with numerical simulations for strain mapping in microstructures and devices, is also presented. Subsequently, temperature-dependent Raman spectra are employed to investigate the crystal anharmonicity and the lattice expansion, with a detailed analysis of the multiple-phonon scattering coefficients, that are then compared with data present in the literature. The temperature dependence of Raman modes is also used to develop Raman thermometry to measure lattice thermal conductivity, in view of the recently proposed use of these materials in integrated opto–thermo-electronic devices. In summary, Raman spectroscopy is demonstrated as an essential tool for metrology and physical insight of the technologically relevant and complex SiGeSn ternary alloy system.

Lattice strain in crystals can be exploited to effectively tune their physical properties. In microscopic structures, experimental access to the full strain tensor with spatial resolution at the (sub‐)micrometer scale is at the same time very interesting and challenging. In this work, how scanning X‐ray diffraction microscopy, an emerging model‐free method based on synchrotron radiation, can shed light on the complex, anisotropic deformation landscape within three dimensional (3D) microstructures is shown. This technique allows the reconstruction of all lattice parameters within any type of crystal with submicron spatial resolution and requires no sample preparation. Consequently, the local state of deformation can be fully quantified. Exploiting this capability, all components of the strain tensor in a suspended, strained Ge _{1 − x} Sn _x /Ge microdisk are mapped. Subtle elastic deformations are unambiguously correlated with structural defects, 3D microstructure geometry, and chemical variations, as verified by comparison with complementary electron microscopy and finite element simulations. The methodology described here is applicable to a wide range of fields, from bioengineering to metallurgy and semiconductor research.