5 results
Search Results
Now showing 1 - 5 of 5
- ItemTemperature dependence of strain–phonon coefficient in epitaxial Ge/Si(001): A comprehensive analysis(Chichester [u.a.] : Wiley, 2020) Manganelli, C.L.; Virgilio, M.; Skibitzki, O.; Salvalaglio, M.; Spirito, D.; Zaumseil, P.; Yamamoto, Y.; Montanari, M.; Klesse, W.M.; Capellini, G.We investigate the temperature dependence of the Ge Raman mode strain–phonon coefficient in Ge/Si heteroepitaxial layers. By analyzing the temperature-dependent evolution of both the Raman Ge-Ge line and of the Ge lattice strain, we obtain a linear dependence of the strain–phonon coefficient as a function of temperature. Our findings provide an efficient method for capturing the temperature-dependent strain relaxation mechanism in heteroepitaxial systems. Furthermore, we show that the rather large variability reported in the literature for the strain–phonon coefficient values might be due to the local heating of the sample due to the excitation laser used in µ-Raman experiments. © 2020 The Authors. Journal of Raman Spectroscopy published by John Wiley & Sons Ltd
- ItemGate-controlled quantum dots and superconductivity in planar germanium([London] : Nature Publishing Group UK, 2018) Hendrickx, N.W.; Franke, D.P.; Sammak, A.; Kouwenhoven, M.; Sabbagh, D.; Yeoh, L.; Li, R.; Tagliaferri, M.L.V.; Virgilio, M.; Capellini, G.; Scappucci, G.; Veldhorst, M.Superconductors and semiconductors are crucial platforms in the field of quantum computing. They can be combined to hybrids, bringing together physical properties that enable the discovery of new emergent phenomena and provide novel strategies for quantum control. The involved semiconductor materials, however, suffer from disorder, hyperfine interactions or lack of planar technology. Here we realise an approach that overcomes these issues altogether and integrate gate-defined quantum dots and superconductivity into germanium heterostructures. In our system, heavy holes with mobilities exceeding 500,000 cm2 (Vs)−1 are confined in shallow quantum wells that are directly contacted by annealed aluminium leads. We observe proximity-induced superconductivity in the quantum well and demonstrate electric gate-control of the supercurrent. Germanium therefore has great promise for fast and coherent quantum hardware and, being compatible with standard manufacturing, could become a leading material for quantum information processing.
- ItemThe thermal stability of epitaxial GeSn layers(Melville, NY : AIP Publ., 2018) Zaumseil, P.; Hou, Y.; Schubert, M.A.; von den Driesch, N.; Stange, D.; Rainko, D.; Virgilio, M.; Buca, D.; Capellini, G.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.
- ItemModeling of edge-emitting lasers based on tensile strained germanium microstrips(New York, NY : IEEE, 2015) Peschka, D.; Thomas, M.; Glitzky, A.; Nürnberg, R.; Gärtner, K.; Virgilio, M.; Guha, S.; Schroeder, T.; Capellini, G.; Koprucki, Th.In this paper, we present a thorough modeling of an edge-emitting laser based on strained germanium (Ge) microstrips. The full-band structure of the tensile strained Ge layer enters the calculation of optical properties. Material gain for strained Ge is used in the 2D simulation of the carrier transport and of the optical field within a cross section of the microstrips orthogonal to the optical cavity. We study optoelectronic properties of the device for two different designs. The simulation results are very promising as they show feasible ways toward Ge emitter devices with lower threshold currents and higher efficiency as published insofar.
- ItemDesign and simulation of losses in Ge/SiGe terahertz quantum cascade laser waveguides(Washington, DC : Soc., 2020) Gallacher, K.; Ortolani, M.; Rew, K.; Ciano, C.; Baldassarre, L.; Virgilio, M.; Scalari, G.; Faist, J.; Gaspare, L.D.I.; Seta, M.D.E.; Capellini, G.; Grange, T.; Birner, S.; Paul, D.J.The waveguide losses from a range of surface plasmon and double metal waveguides for Ge/Si1-xGex THz quantum cascade laser gain media are investigated at 4.79 THz (62.6 µm wavelength). Double metal waveguides demonstrate lower losses than surface plasmonic guiding with minimum losses for a 10 µm thick active gain region with silver metal of 21 cm-1 at 300 K reducing to 14.5 cm-1 at 10 K. Losses for silicon foundry compatible metals including Al and Cu are also provided for comparison and to provide a guide for gain requirements to enable lasers to be fabricated in commercial silicon foundries. To allow these losses to be calculated for a range of designs, the complex refractive index of a range of nominally undoped Si1-xGex with x = 0.7, 0.8 and 0.9 and doped Ge heterolayers were extracted from Fourier transform infrared spectroscopy measurements between 0.1 and 10 THz and from 300 K down to 10 K. The results demonstrate losses comparable to similar designs of GaAs/AlGaAs quantum cascade laser plasmon waveguides indicating that a gain threshold of 15.1 cm-1 and 23.8 cm-1 are required to produce a 4.79 THz Ge/SiGe THz laser at 10 K and 300 K, respectively, for 2 mm long double metal waveguide quantum cascade lasers with facet coatings. © 2020 OSA - The Optical Society. All rights reserved.