This paper presents an in-depth evaluation of 1130 nm VCSEL devices, including single emitters and arrays produced using industrial III-V semiconductor fabrication processes. The study focuses on electro-optical performance and device longevity, revealing wall plug efficiencies of approximately 32% at 25 degrees C for single junction devices. A detailed comparison between polarization-stabilized and non-stabilized devices highlights that polarization-stabilized VCSELs maintain a consistent polarization extinction ratio of around -15 dB, regardless of their modal behavior. Additionally, we introduce a model predicting the scaling of arrays to achieve watt-level power outputs, optimizing optical aperture, pitch, and mesa count for specific applications. This analysis underlines the potential of these devices for advanced sensing and data transmission applications.

We present comprehensive modeling of a SiGeSn multi-quantum well laser that has been previously experimentally shown to feature an order of magnitude reduction in the optical pump threshold compared to bulk lasers. We combine experimental material data obtained over the last few years with k · p theory to adapt transport, optical gain, and optical loss models to this material system (drift-diffusion, thermionic emission, gain calculations, free carrier absorption, and intervalence band absorption). Good consistency is obtained with experimental data, and the main mechanisms limiting the laser performance are discussed. In particular, modeling results indicate a low non-radiative lifetime, in the 100 ps range for the investigated material stack, and lower than expected Γ-L energy separation and/or carrier confinement to play a dominant role in the device properties. Moreover, they further indicate that this laser emits in transverse magnetic polarization at higher temperatures due to lower intervalence band absorption losses. To the best of our knowledge, this is the first comprehensive modeling of experimentally realized SiGeSn lasers, taking the wealth of experimental material data accumulated over the past years into account. The methods described in this paper pave the way to predictive modeling of new (Si)GeSn laser device concepts.

We report on the design of a waveguide coupled GeSn microdisk-laser cavity in which the germanium virtual substrate serving as a template for GeSn growth is repurposed for the definition of passive on-chip interconnection waveguides.

This thesis analyses how public decision-makers can rapidly and sustainably decarbonise their regions, considering the challenge that promoting timely decarbonisation represents. The research was d ...

The recent rise of GeSn-based optically pumped lasers have multiplied the efforts to fabricate a fully CMOS compatible and group IV-based light emitter. Their integration with Si-based electronics may yield heavily reduced power consumption in integrated circuits and pave the way towards new sensing or medical applications. Here, we discuss the epitaxy of group IV GeSn and SiGeSn semiconductors and show their suitability for light emitting applications. Double and multi quantum well heterostructures are evaluated, whereby the latter enables an inherently easier control over the formation of deleterious misfit defects. Consequently, microdisk lasers fabricated from those show greatly enhanced light emission and reduced lasing thresholds. The use of in-situ p-i-n doping schemes allow the formation of light emitting diodes, resulting in electrically-enabled light emission already at room temperature.

In recent years much effort has been made to increase the Sn content in GeSn alloys in order to increase direct bandgap charge carrier recombination and, therefore, to reach room temperature lasing. While being successful for the former, the increase of Sn content is detrimental, leading to increased defect concentrations and a lower thermal budget regarding processing. In this work we demonstrate strong photoluminescence enhancement in low Sn content Ge0.94Sn0.06 layers by implementing tensile strain. Fitting of the calculated photoluminescence spectra to reproduce our experimental results indicates a strain of ~1.45%, induced via an SiNx stressor layer, which is strong enough to transform the investigated layer into a direct bandgap semiconductor. Moreover, theoretical calculations, using the 8-band k·p model, show the advantages of using low Sn content tensile strained GeSn layers in respect to gain and lasing temperature. We show that low Sn content GeSn alloys have a strong potential to enable efficient room temperature lasers on electronic-photonic integrated circuits.

GeSn is discussed as solution to realize the dream of a group IV light source integrated on a Si chip. Sn added into a Ge lattice decreases the conduction band energies leading to a direct bandgap semiconductor band structure. However, the compressive strain increases the direct band energy imposing a large Sn content in the GeSn bulk. In spite of many difficulties regarding the growth of epitaxial GeSn alloys on Si, several hundred nm thick GeSn layers with various Sn concentrations up to 15% could be realized and used as gain material for lasers. Nowadays research concentrates on increasing the Sn content towards 20 at% as well as structural layout. The challenge here is the decreasing quality at high Sn contents and the isolation of the active layer from the mists formed at the interface with Ge/Si which increase the laser threshold. In this direction we discuss the influence on lasing and threshold of MQW SiGeSn/GeSn heterostructures with different quantum well thicknesses. Other solution proposed is the change of intrinsic strain type from compressive into tensile by introducing Si3N4 stressors and also GeSn on Insulator technology. These methods are well known in CMOS technology and can be applied to very low Sn content GeSn alloys. The discussion on the best way to reach room temperature laser is addressed both theoretical and experimental.

The recent development of optically pumped lasers made from Si-congruent GeSn alloys have strengthened the efforts to fabricate a monolithically integratable light source. Such fully Si-compatible solution may allow merging of state-of-the-art electronics with photonic components on the same chip for on-chip optical interconnects. To advance this prospering field, we investigated the epitaxy of different GeSn/SiGeSn heterostructures, based on GeSn active layers. Double heterostructures allow confinement of carriers in GeSn, though with the deleterious presence of misfit dislocations in the rather thick active regions. This can be overcome, however, in multi quantum well (MQW) structures. Microdisk resonators made from different heterostructures were fabricated, indicating enhanced properties of MQW layers. Epitaxy of in-situ doped p-i-n heterostructure diodes shows paths towards electrical carrier injection into GeSn optoelectronic devices.

GeSn/SiGeSn multiple quantum well structures have been grown by means of low temperature reactive gas source epitaxy on Ge pseudosubstrates. The MQW structures exhibit type I band alignment. Optically pumped μ-disc laser exhibit a threshold of 40kW/cm 2 to obtain optically pumped lasing.

We will present modeling of experimentally demonstrated SiGeSn multi-quantum well lasers. In particular, the impact of radiative recombination lifetime reduction in multi-quantum wells as well as temperature dependent L-valley electron concentrations will be shown to yield adequate modeling of these devices. Models will be further extrapolated to yield performance requirements for electrically pumped and room temperature lasing operation.

The electrical and optical material properties of epitaxial Ge1−xSnx and SiyGe1−x−ySnx are of high interest for novel device applications. However, the limited Sn solubility in Ge makes the epitaxial growth of Ge1−xSnx and SiyGe1−x−ySnx challenging. Most of the literature describing the epitaxial growth is for Ge2H6 and SnCl4 as Ge and Sn precursors, respectively. A more recent publication deals with the epitaxial growth of high-quality Ge1−xSnx with the more conventional GeH4. In this manuscript, we compare the structural and optical material quality of Ge1−xSnx, epitaxially grown on Ge virtual substrates as a function of growth pressure, growth temperature, the choice of the carrier gas (H2 or N2) and the choice of the Ge precursor (GeH4 versus Ge2H6). The best material quality in terms of surface morphology and photoluminescence characteristics is obtained if GeH4 is used as a Ge precursor. For Ge1−xSnx grown with Ge2H6 and at atmospheric pressure, pyramidical defects can be seen and there is a risk for uncontrolled local Sn agglomeration. The pyramidical defects are not observed on Ge1−xSnx layers grown at reduced pressure, but the highest achievable substitutional Sn concentration is lower. No pyramidical defects are found for Ge1−xSnx layers grown with GeH4 and the issue of uncontrolled local Sn agglomeration does not appear.

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 and 1550 nm yields comparable lasing thresholds. The design with multi quantum wells reduces the lasing threshold to 40 ± 5 kW/cm2 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.

We report on the direct observation of lattice relaxation and Sn segregation of GeSn/Ge/Si heterostructures under annealing. We investigated strained and partially relaxed epi-layers with Sn content in the 5 at. %-12 at. % range. In relaxed samples, we observe a further strain relaxation followed by a sudden Sn segregation, resulting in the separation of a β-Sn phase. In pseudomorphic samples, a slower segregation process progressively leads to the accumulation of Sn at the surface only. The different behaviors are explained by the role of dislocations in the Sn diffusion process. The positive impact of annealing on optical emission is also discussed.

Since the first demonstration of lasing in direct bandgap GeSn semiconductors, the research efforts for the realization of electrically pumped group IV lasers monolithically integrated on Si have significantly intensified. This led to epitaxial studies of GeSn/SiGeSn hetero- and nanostructures, where charge carrier confinement strongly improves the radiative emission properties. Based on recent experimental literature data, in this report we discuss the advantages of GeSn/SiGeSn multi quantum well and quantum dot structures, aiming to propose a roadmap for group IV epitaxy. Calculations based on 8-band k∙p and effective mass method have been performed to determine band discontinuities, the energy difference between Γ- and L-valley conduction band edges, and optical properties such as material gain and optical cross section. The effects of these parameters are systematically analyzed for an experimentally achievable range of Sn (10 to 20 at.%) and Si (1 to 10 at.%) contents, as well as strain values (−1 to 1%). We show that charge carriers can be efficiently confined in the active region of optical devices for experimentally acceptable Sn contents in both multi quantum well and quantum dot configurations.

Peter Grünberg Institute (PGI 9) and JARA-Fundamentals of Future Information Technologies, Forschungszentrum Juelich, 52425, Germany. 2 Central Institute for Engineering, Electronics and Analytics – Analytics, Forschungszentrum Juelich, Germany CEA, LETI, MINATEC Campus and Univ. Grenoble Alpes, France. IHP, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany Department of Sciences, Università Roma Tre, Viale G. Marconi, 446, 00146 Roma, Italy Institute of Microwaves and Photonics, School of Electronic and Electrical Engineering, University of Leeds, UK

Growth and characterization of advanced group IV semiconductor materials with CMOS-compatible applications are demonstrated, both in photonics. The investigated GeSn/SiGeSn heterostructures combine direct bandgap GeSn active layers with indirect gap ternary SiGeSn claddings, a design proven its worth already decades ago in the III-V material system. Different types of double heterostructures and multi-quantum wells (MQWs) are epitaxially grown with varying well thicknesses and barriers. The retaining high material quality of those complex structures is probed by advanced characterization methods, such as atom probe tomography and dark-field electron holography to extract composition parameters and strain, used further for band structure calculations. Special emphasis is put on the impact of carrier confinement and quantization effects, evaluated by photoluminescence and validated by theoretical calculations. As shown, particularly MQW heterostructures promise the highest potential for efficient next generation complementary metal-oxide-semiconductor (CMOS)-compatible group IV lasers.

In this paper we present a systematic study of GeSn n-FETs. First, process modules such as high-k metal gate stacks and NiGeSn - metallic contacts for use as source/drain contacts are characterized and discussed. GeSn alloys of different Sn content allow the study of the capacitance-voltage (CV) and contact characteristics of both direct and indirect bandgap semiconductors. We then present GeSn n-FET devices we have fabricated. The device characterization includes temperature dependent IV characteristics. As important step towards GeSn for tunnel-FET Ge0.87Sn0.13 tunnel-diodes with negative differential resistance at reduced temperature are shown. The present work provides a base for further optimization of GeSn FET and novel tunnel FET devices.

The amount of data collected, transferred and processed increased over the last decade with a substantial annual rate. With the internet of things in sight, this trend will be continued. Already today more than 10% of the electrical power produced in the western world is consumed by IT products, underlining the demand to drastically reduce the power consumption. In fact, energy consumption will be the main driver of development in information technology. Silicon photonics is considered to be an attractive pathway to drastically reduce power consumption in information technology based on classical Si microelectronics /1/. Moreover Si photonics are envisioned also as a promising pathway towards quantum computing/2/. Group IV alloys, namely Ge and SiGe on Si, are heavily investigated for the integration of modulators and detectors on Si. However, higher integration levels of optical data transfer on the chip will require the integration of low power laser. The latter is approached by a wide range of technologies to deposit III/V structures on Si as well as by bonding III/V lasers Si. Recently, a direct bandgap as well as optically pumped lasing was demonstrated for GeSn alloys deposited on Ge virtual substrates on Si (100) 8” wafers. Here, efforts are reported of this ongoing endeavor towards an electrically pumped group IV laser. The group IV alloy GeSn provide a direct band gap for Sn concentration above ~8%, which is far beyond the solid solubility limit of ~1%. Recently high quality GeSn alloys with Sn concentrations up to 14.5% could be grown at low temperatures and high growth rates by means reactive gas source epitaxy. These GeSn have a direct band gap, in the range of 0.48-0.63 eV dependening on the Sn concentration. Phosphorous and Boron doping has been realized to fabricate p-i-n junction in SiGeSn/GeSn structures. Thus these materials pave the road for the integration of optoelectronic circuitry on Si (100) substrates. Optically pumped laser in the Fabry Perot geometry as well as microdisc lasers have been fabricated from GeSn films, SiGeSn double heterostructures and SiGeSn/GeSn multiple quantum wells (MQW) on Ge virtual substrates. The threshold required to achieve lasing dropped from ~300 kW/cm2 for a thick GeSn film to about 30 kW/cm2 for a MQW structure. This can be attributed to reduced optical losses due to surface scattering as well as due to the reduced number of states in the multiple quantum wells, which allows carrier inversion at smaller pumping powers. However, due to the very small effective mass of electrons in the Г valley compared to large mass in the L valley, the quantum wells have to be designed carefully. For thin quantum wells the confinement shift of the subbands of the Г valley is larger than that for the L valley reducing the directness and may even turn it into an indirect material. Moreover, a (Si)GeSn buffer layer above critical thickness is required to relax the strain before the growth of the active region of the laser. The strain relaxation occurs predominantly via 90° step edge dislocations at the Ge/GeSn interface, within the hetero- and MQW structures no dislocations were detected by cross sectional TEM. However, besides defect engineering, care has to be taken in the design of the structures also to avoid losses due to absorption in GeSn and SiGeSn cladding layers, since the limited band offsets give rather stringent design rules. To achieve electrically pumped lasing double hetero- and MQW-structures have been grown using SiGeSn cladding and barrier layers. Parts of the SiGeSn cladding layers have been doped by P and B to achieve p-i-n junctions. First devices have been fabricated showing a superior electroluminescence efficiency of MQW structures compared to hetero- of homojunction devices. /1/ R. Soref, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, 12, 1678 (2006) /2/ T. Rudolph APL PHOTONICS 2, 030901 (2017)

SiGeSn ternaries are grown on Ge‐buffered Si wafers incorporating Si or Sn contents of up to 15 at%. The ternaries exhibit layer thicknesses up to 600 nm, while maintaining a high crystalline quality. Tuning of stoichiometry and strain, as shown by means of absorption measurements, allows bandgap engineering in the short‐wave infrared range of up to about 2.6 µm. Temperature‐dependent photoluminescence experiments indicate ternaries near the indirect‐to‐direct bandgap transition, proving their potential for ternary‐based light emitters in the aforementioned optical range. The ternaries' layer relaxation is also monitored to explore their use as strain‐relaxed buffers, since they are of interest not only for light emitting diodes investigated in this paper but also for many other optoelectronic and electronic applications. In particular, the authors have epitaxially grown a GeSn/SiGeSn multiquantum well heterostructure, which employs SiGeSn as barrier material to efficiently confine carriers in GeSn wells. Strong room temperature light emission from fabricated light emitting diodes proves the high potential of this heterostructure approach.