The strong correlation between advancing the performance of Si microelectronics and their demand of low power consumption requires new ways of data communication. Photonic circuits on Si are already highly developed except for an eligible on-chip laser source integrated monolithically. The recent demonstration of an optically pumped waveguide laser made from the Si-congruent GeSn alloy, monolithical laser integration has taken a big step forward on the way to an all-inclusive nanophotonic platform in CMOS. We present group IV microdisk lasers with significant improvements in lasing temperature and lasing threshold compared to the previously reported nonundercut Fabry−Perot type lasers. Lasing is observed up to 130 K with optical excitation density threshold of 220 kW/cm 2 at 50 K. Additionally the influence of strain relaxation on the band structure of undercut resonators is discussed and allows the proof of laser emission for a just direct Ge 0.915 Sn 0.085 alloy where Γ and L valleys have the same energies. Moreover, the observed cavity modes are identified and modeled.

The recent observation of a fundamental direct bandgap for GeSn group IV alloys and the demonstration of low temperature lasing provide new perspectives to the fabrication of Si photonic circuits. This work addresses the progress in GeSn alloy epitaxy aiming at room temperature GeSn lasing. Chemical vapor deposition of direct bandgap GeSn alloys with a high -to L-valley energy separation and large thicknesses for efficient optical mode confinement is presented and discussed. Up to 1 µm thick GeSn layers with Sn contents up to 14 at.% were grown on thick relaxed Ge buffers, using Ge 2 H 6 and SnCl 4 precursors. Strong strain relaxation (up to 81 %) at 12.5 at.% Sn concentration, translating into an increased separation between -and L-valleys of about 60 meV, have been obtained without crystalline structure degradation, as revealed by Rutherford backscattering/ion channeling spectroscopy and Transmission Electron Microscopy. Room temperature transmission/reflection and photoluminescence measurements were performed to probe the optical properties of these alloys. The emission/absorption limit of GeSn alloys can be extended up to 3.5 µm (0.35 eV), making those alloys ideal candidates for optoelectronics in the mid-infrared region. Theoretical net gain calculations indicate that large room temperature laser gains should be reachable even without additional doping.

A comprehensive study of optical transitions in direct bandgap Ge 0.875 Sn 0.125 group IV alloys via photoluminescence measurements as a function of temperature, compressive strain and excitation power is performed. The analysis of the integrated emission intensities reveals a strain-dependent indirect-to-direct bandgap transition, in good agreement with band structure calculations based on 8 band k•p and deformation potential method. We have observed and quantified  valley -heavy hole and  valley -light hole transitions at low pumping power and low temperatures in order to verify the splitting of the valence band due to strain. We will demonstrate that the intensity evolution of these transitions supports the conclusion about the fundamental direct bandgap in compressively strained GeSn alloys. The presented investigation, thus, demonstrates that direct bandgap group IV alloys can be directly grown on Ge-buffered Si(001) substrates despite their residual compressive strain.2 KEYWORDS: direct bandgap, photoluminescence, germanium tin, group IV, compressive strain TOC GRAPHIC 3 Group IV semiconductors are known for their excellent electronic transport properties but limited optical applicability due to their indirect bandgap nature, turning them into inefficient light emitters. However, the pioneering work of R.Soref and C.H. Perry 1 and, later He and Atwater 2 as well as subsequent theoretical studies [3][4][5] indicated that alloying two group IV elements, i.e. semiconducting Ge and semimetallic -Sn, should result in a group IV semiconductor which could be tuned from a fundamental indirect to a direct bandgap material by increasing the substitutional Sn concentration in the Ge lattice. Although it was unanimously accepted that the -valley of the conduction band can be decreased below the Lvalley, theoretical estimates of the required Sn content for this transition as well as the impact of strain on the transition are widely spread. 6,7 This prospect has driven large efforts to grow device-grade GeSn epilayers, [8][9][10][11] prove their fundamental direct bandgap and finally to demonstrate photonic functionality. Recently, advances in Chemical Vapor Deposition (CVD)of GeSn binaries with high Sn contents of up to 14% has been reported 9,10,12-15 which enabled not only the proof of the direct bandgap nature but also the unambiguous demonstration of laser action at 2.3 µm under optical pumping. 16 Hence, direct bandgap GeSn alloys are CMOS-compatible IV-IV semiconductors with novel optical and electrical properties that are similar to those of III-V and II-VI compounds, used today in optoelectronic applications, i.e. The growth temperature (350°C), the total pressure and the partial pressures of the source gases were kept constant, resulting in the growth of GeSn alloys with a Sn content of 12.5 ± 0.5%. 11,15 Due to the lattice mismatch between the GeSn film and Ge virtual substrate, the GeSn layers were biaxially compressively strained. The films are fully strained for thicknesses below the critical t...

GeSn and SiGeSn are promising materials for the fabrication of a group IV laser source offering a number of design options from bulk to heterostructures and quantum wells. Here, we investigate GeSn/SiGeSn multi quantum wells using the optically pumped laser effect. Three complex heterostructures were grown on top of 200 nm thick strain relaxed Ge0.9Sn0.1 buffers. The lasing is investigated in terms of threshold and maximal lasing operation temperature by comparing multiple quantum well to double heterostructure samples. Pumping under two different wavelengths of 1064 nm and 1550 nm yield comparable lasing thresholds. The design with multi quantum wells reduces the lasing threshold to (40 ± 5) kW/cm 2 at 20 K, almost 10 times lower than for bulk structures. Moreover, 20 K higher maximal lasing temperatures were found for lower energy pumping of 1550 nm.

Group IV photonics is on the way to be integrated with electronic circuits, making information transfer and processing faster and more energy efficient. Light sources, a critical component of photonic integrated circuits, are still in development. Here, we compare Multi-Quantum-Well (MQW) light emitting diodes (LEDs) with Ge0.915Sn0.085 wells and Si0.1Ge0.8Sn0.1 to a reference Ge0.915Sn0.085 homojunction LED. Material properties as well as band structure calculations are discussed, followed by optical investigations. Electroluminescence spectra acquired at various temperatures indicate an effective carrier confinement for electrons and holes in the GeSn quantum wells and confirm the excellent performance of GeSn/SiGeSn MQW light emitters.