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Achieving high crystalline quality germanium‐tin (Ge1 − xSnx) semiconductors at Sn content exceeding 10% is quintessential to implement the long sought‐after silicon‐compatible mid‐infrared photonics. Herein, by using sub‐20 nm Ge nanowires as compliant growth substrates, Ge1 − xSnx alloys with a Sn content of 18% exhibiting a high composition uniformity and crystallinity along a few micrometers in the nanowire axial direction are demonstrated. The measured bandgap energy of the Ge/Ge0.82Sn0.18 core/shell nanowires is 0.322 eV enabling the mid‐infrared photodetection with a cutoff wavelength of 3.9 µm. These narrow bandgap nanowires are also integrated into top‐gated field‐effect transistors and phototransistors. Depending on the gate design, these transistors are found to exhibit either ambipolar or unipolar behavior with a subthreshold swing as low as 228 mV/decade at 85 K. Moreover, varying the top gate voltage from ‐1 to 5 V yields nearly one order of magnitude increase in the photocurrent of the nanowire phototransistor under a 2330 nm illumination. This study shows that the core/shell nanowire architecture with a very thin core not only mitigates the challenges associated with strain build‐up observed in thin films but also provides a promising platform for all‐group IV mid‐infrared photonics and nanoelectronics paving the way toward sensing and imaging applications. [ABSTRACT FROM AUTHOR]

GeSn alloys are a promising emerging complementary metal–oxide–semiconductor compatible technology for applications in photonics and electronics. However, the unavoidable intrinsic compressive strain introduced during epitaxial growth has prevented researchers from pushing the performance of GeSn devices to the limit and realizing real-world applications. In this paper, we present a straightforward geometric strain-inversion technique that harnesses the harmful compressive strain to achieve beneficial tensile strain in GeSn nanowires, drastically increasing the directness of the band structure. We achieve ∼2.67% uniaxial tensile strain in ∼120 nm wide nanowires, surpassing other values reported thus far. Unique pseudo-superlattices comprising of indirect and direct bandgap GeSn are demonstrated in a single material only by applying a periodic tensile strain. Improved directness in tensile-strained GeSn significantly enhances the photoluminescence by a factor of ∼2.5. This work represents a way to develop scalable band-engineered GeSn nanowire devices with lithographic design flexibility. This technique can be potentially applied to any layer with an intrinsic compressive strain, creating opportunities for unique tensile strained materials with diverse electronic and photonic applications. [ABSTRACT FROM AUTHOR]

Recent development on Ge1−xSnx nanowires with high Sn content, beyond its solid solubility limit, makes them attractive for all group-IV Si-integrated infrared photonics at the nanoscale. Herein, we report a chemical vapor deposition-grown high Sn-content Ge–Ge0.92Sn0.08 core–shell based single nanowire photodetector operating at the optical communication wavelength of 1.55 μm. The atomic concentration of Sn in nanowires has been studied using x-ray photoelectron and Raman spectroscopy data. A metal–semiconductor–metal based single nanowire photodetector, fabricated via an electron beam lithography process, exhibits significant room-temperature photoresponse even at zero bias. In addition to the high-crystalline quality and identical shell composition of the nanowire, the efficient collection of photogenerated carriers under an external electric field results in the superior responsivity and photoconductive gain as high as ∼70.8 A/W and ∼57, respectively, at an applied bias of −1.0 V. The extra-ordinary performance of the fabricated photodetector demonstrates the potential of GeSn nanowires for future Si CMOS compatible on-chip optical communication device applications. [ABSTRACT FROM AUTHOR]

GeSn alloys are promising candidates for complementary metal‐oxide‐semiconductor‐compatible, tunable lasers. Relaxation of residual compressive strain in epitaxial GeSn has recently shown promise in improving the lasing performance. However, the suspended device configuration that is thus far introduced to relax the strain is destined to limit heat dissipation, thus hindering the device performance. Herein is demonstrated that strain‐free GeSn microdisk laser devices fully released on Si outperform the canonical suspended devices. This approach allows to simultaneously relax the limiting compressive strain while offering excellent thermal conduction. Optical simulations confirm that, despite a relatively small refractive index contrast between GeSn and Si, optical confinement in strain‐free GeSn optical cavities on Si is superior to that in conventional strain‐free GeSn cavities suspended in the air. Moreover, thermal simulations indicate a negligible temperature increase in the device. Conversely, the temperature in the suspended devices increases substantially reaching, for instance, 120 K at a base temperature of 75 K under the employed optical pumping conditions. Such improvements enable increasing the operation temperature by ≈40 K and reducing the lasing threshold by 30%. This approach lays the groundwork to implement new designs in the quest for room temperature GeSn lasers on Si. [ABSTRACT FROM AUTHOR]

GeSn alloys have been regarded as a potential lasing material for a complementary metal–oxide–semiconductor-compatible light source. Despite their remarkable progress, all GeSn lasers reported to date have large device footprints and active areas, which prevent the realization of densely integrated on-chip lasers operating at low power consumption. Here, we present a 1D photonic crystal nanobeam with a very small device footprint of 7 μm2 and a compact active area of ∼1.2 μm2 on a high-quality GeSn-on-insulator substrate. We also report that the improved directness in our strain-free nanobeam lasers leads to a lower threshold density and a higher operating temperature compared to the compressive strained counterparts. The threshold density of the strain-free nanobeam laser is ∼18.2 kW cm−2 at 4 K, which is significantly lower than that of the unreleased nanobeam laser (∼38.4 kW cm−2 at 4 K). Lasing in the strain-free nanobeam device persists up to 90 K, whereas the unreleased nanobeam shows quenching of lasing at a temperature of 70 K. Our demonstration offers an avenue toward developing practical group-IV light sources with high-density integration and low power consumption. [ABSTRACT FROM AUTHOR]

Semiconductor membranes emerged as a versatile class of nanomaterials to control lattice strain and engineer complex heterostructures enabling a variety of innovative applications. With this perspective, herein this platform is exploited to tune simultaneously the lattice parameter and bandgap energy in group IV GeSn semiconductor alloys. As Sn content is increased to reach a direct bandgap, these semiconductors become metastable and typically compressively strained. It is shown that the relaxation in released membranes extends the absorption wavelength range deeper in the mid‐infrared. Fully released Ge0.83Sn0.17 membranes are integrated on silicon and used in the fabrication of broadband photodetectors operating at room temperature with a record wavelength cutoff of 4.6 µm, without compromising the performance at shorter wavelengths down to 2.3 µm. These membrane devices are characterized by two orders of magnitude reduction in dark current as compared to as‐grown strained epitaxial layers. A variety of experimental tools and optimized calculations are used to discuss the crystalline quality, composition uniformity, lattice strain, and the electronic band structure of the investigated materials and devices. The ability to engineer all‐group IV transferable mid‐infrared photodetectors lays the groundwork to implement scalable and flexible sensing and imaging technologies exploiting these integrative, silicon‐compatible strained‐relaxed GeSn membranes. [ABSTRACT FROM AUTHOR]

The thermal budget is highly critical in processing the emerging group IV Silicon-Germanium-Tin (SiGeSn) optoelectronic devices. These emerging semiconductors exhibit a fundamental direct bandgap covering the mid-infrared range at Sn contents above 10 at. %, which is an order of magnitude higher than the equilibrium solubility. Consequently, the device processing steps must be carried out at temperatures low enough to prevent the degradation of these metastable layers. However, conventional optoelectronic device fabrication methods often require the deposition of dielectric layers at temperatures reaching 400 °C. Although this temperature can be sustained in processing a variety of devices, yet it is sufficiently high to damage GeSn and SiGeSn device structures. With this perspective, the authors investigated the morphological and optical properties of tetraethylorthosilicate (TEOS) layers as an alternative material to conventional dielectric layers. Spin-on-glass deposition on an Si wafer with baking temperatures in the 100–150 °C range leads to high homogeneity and low surface roughness of the TEOS layer. The authors show that the TEOS optical transmission is higher than 90% from visible to mid-infrared wavelengths (0.38–8 μm), combined with the analysis of the real and complex part of the refractive index. Furthermore, the TEOS deposition on GeSn and SiGeSn samples does not affect the material crystallinity or induces clustering of Sn atoms. Therefore, the low deposition temperature and high transparency make TEOS an ideal material for the integration of metastable GeSn and SiGeSn semiconductors in the fabrication of mid-infrared photonic devices. [ABSTRACT FROM AUTHOR]

We present structural characterization of the wurtzite crystal structure of GaP nanowires, which were recently shown to have a direct electronic band gap. The structural parameters of the wurtzite phase do consist of two lattice parameters and one internal degree of freedom, determining the Ga-P bond length along the c direction. Using density functional theory calculations, we study the influence of the internal degree of freedom on the band structure. By synchrotron x-ray diffraction studies near the Ga-k edge we determine the lattice parameters a = 3.8419 Å and c = 6.3353 Å as well as the internal degree of freedom u = 0.37385 with high accuracy. We find that different Ga-P bond lengths are not equal, in contrast to the case in the zinc blende bulk phase. As a result, a spontaneous polarization is predicted for wurtzite GaP. [ABSTRACT FROM AUTHOR]