We report on the behavior of Ge-Ge, Ge-Sn, Sn-Sn like and disorder-activated vibrational modes in GeSn semiconductors investigated using Raman scattering spectroscopy. By using an excitation wavelength close to E1 gap, all modes are clearly resolved and their evolution as a function of strain and Sn content is established. In order to decouple the individual contribution of content and strain, the analysis was conducted on series of pseudomorphic and relaxed epitaxial layers with a Sn content in the 5-17at.% range. All vibrational modes display qualitatively the same behavior as a function of content and strain, viz. a linear downshift as the Sn content increases or the compressive strain relaxes. Simultaneously, Ge-Sn and Ge-Ge peaks broaden, and the latter becomes increasingly asymmetric. This asymmetry, coupled with the peak position, is exploited to implement an empirical approach to accurately quantify the Sn composition and lattice strain from Raman spectra.Understanding the behavior of different vibrational modes in a semiconductor is of paramount importance to probe its crystal phase and symmetry, composition, lattice strain, isotopic content, electronic and phononic properties. [1][2][3] In this regard, Raman scattering spectroscopy has thus become an ubiquitous characterisation technique as information-rich spectra are acquired from straightforward and non-destructive measurements. Therefore, it is commonly used to evaluate the chemical composition and lattice properties of, for instance, group-IV semiconductors such as strained Si, 4-6 strained Ge, 7-10 SiGe, [11][12][13][14] and GeSn layers. [15][16][17][18][19][20][21][22][23][24][25] The latter are particularly of growing interest because of their relevance to Si-compatible light emission and detection applications in the short-and mid-wavelength infrared, [26][27][28][29][30][31][32][33][34][35] which can lead to the integration of optoelectronic and photonic circuits on complementary metal-oxide-semiconductor (CMOS) platforms. [36][37][38] Previous reports on the vibrational modes of GeSn mainly focused on Ge-Ge longitudinal optical (LO) mode as the analyses relied on the use of 488 nm 15,16 or 532 nm 18-24 excitation lines. Under these conditions, the signal-to-noise ratio is too low to clearly distinguish Sn-related vibrational modes in the vicinity of the more prominent Ge-Ge LO peak. This also applies to the study of ternary SiGeSn semiconductors. [39][40][41] When using a 633 nm excitation laser, the signal-tonoise ratio is significantly enhanced, thus allowing a clear distinction of Ge-Ge and Ge-Sn modes, in addition to other features such as disorder-activated (DA) and Sn-Sn like modes. This higher sensitivity is attributed to the increase in Raman scattering cross section when the excitation wavelength becomes close to the material's E1 gap. 39,42 Oehme et al. 25 and D'Costa et al. 17 provided a quantitative description of the evolution of peak positions as a function of the composition. However, in these studies, the investigated sampl...

van der Waals (vdW) heterostructures have recently been introduced as versatile building blocks for a variety of novel nanoscale and quantum technologies. Harnessing the unique properties of

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Engineering light absorption in the extended short-wave infrared (e-SWIR) range using scalable materials is a long-sought-after capability that is crucial to implement cost-effective and highperformance sensing and imaging technologies. Herein, we demonstrate enhanced, tunable e-SWIR absorption using silicon-integrated platforms consisting of ordered arrays of metastable GeSn nanowires with Sn content reaching 9 at.% and variable diameters. Detailed simulations were combined with experimental analyses to systematically investigate light-GeSn nanowire interactions to tailor and optimize the nanowire array geometrical parameters and the corresponding optical response. The diameter-dependent leaky mode resonance peaks are theoretically predicted and experimentally confirmed with a tunable wavelength from 1.5 to 2.2 μm. A three-fold enhancement in the absorption with respect to GeSn layers at 2.1 µm was achieved using nanowires with a diameter of 325 nm. Finite difference time domain simulations unraveled the underlying mechanisms of the e-SWIR enhanced absorption. Coupling of the HE11 and HE12 resonant modes to nanowires is observed at diameters above 325 nm, while at smaller diameters and longer wavelengths the HE11 mode is guided into the underlying Ge layer. The presence of tapering in NWs further extends the absorption range while minimizing reflection. This ability to engineer and enhance e-SWIR absorption lays the groundwork to implement novel photonic devices exploiting all-group IV platforms.

van der Waals epitaxy is an attractive alternative to direct heteroepitaxial growth of semiconductor materials where the forced coherency at the interface cannot sustain large differences in lattice parameters and thermal expansion coefficients between the substrate and the epilayer. In this work, we demonstrate the growth of monocrystalline InP on Ge and SiO 2 /Si substrates using graphene as an interfacial layer. Micron-sized InP crystals were found to grow with interfaces of high crystalline quality. Depending on the growth conditions, these crystals coalesce to form continuous film-like structures. This coalescence is more pronounced on asgrown graphene layers as compared to transferred ones. Some InP crystals were found to possess a polytypic structure, consisting of zinc-blende and wurtzite phases. We demonstrate that the zinc-blende and wurtzite close packed structures form a type-II homojunction with well (barrier) width of about 10 nm. The optical properties, investigated using room temperature nanocathodoluminescence, indicated the signatures of the direct optical transitions at 1.34 eV across the gap of the zinc-blende phase and the indirect transitions at ~1.31 eV originating from the close packed phase. In addition to crystals, we also observed InP nanorods growing mainly on graphene transferred onto SiO 2 /Si substrate. These nanorods showed optical transition across the gap of the wurtzite phase at ~1.42 eV. This demonstration of InP direct growth on graphene and the correlative study between the structure and optical properties pave the way to develop InP-graphene hybrid structures for potential applications in integrated photonic and optoelectronic devices.