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1. Asymmetric-coupled Ge/SiGe quantum wells for second harmonic generation at 7.1 THz in integrated waveguides: a theoretical study

Author

Talamas Simola Enrico, Ortolani Michele, Di Gaspare Luciana, Capellini Giovanni, De Seta Monica, and Virgilio Michele

Subjects
second harmonic generation, terahertz, ge/sige quantum wells, non linear waveguide, silicon photonics, Physics, QC1-999
Abstract

We present a theoretical investigation of guided second harmonic generation at THz frequencies in SiGe waveguides embedding n-type Ge/SiGe asymmetric coupled quantum wells to engineer a giant second order nonlinear susceptibility. A characteristic of the chosen material system is the existence of large off-diagonal elements in the χ 2 tensor, coupling optical modes with different polarization. To account for this effect, we generalize the coupled-mode theory, proposing a theoretical model suitable for concurrently resolving every second harmonic generation interaction among guide-sustained modes, regardless of which χ 2 tensor elements it originates from. Furthermore, we exploit the presence of off-diagonal χ 2 elements and the peculiarity of the SiGe material system to develop a simple and novel approach to achieve perfect phase matching without requiring any fabrication process. For a realistic design of the quantum heterostructure we estimate second order nonlinear susceptibility peak values of ∼7 and ∼1.4 × 105 pm/V for diagonal and off diagonal χ 2 elements, respectively. Embedding such heterostructure in Ge-rich SiGe waveguides of thicknesses of the order of 10–15 μm leads to second harmonic generation efficiencies comprised between 0.2 and 2 %, depending on the choice of device parameters. As a case study, we focus on the technologically relevant frequency of 7.1 THz, yet the results we report may be extended to the whole 5–20 THz range.

Published
2024
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2. High-quality CMOS compatible n-type SiGe parabolic quantum wells for intersubband photonics at 2.5–5 THz

Author

Campagna Elena, Talamas Simola Enrico, Venanzi Tommaso, Berkmann Fritz, Corley-Wiciak Cedric, Nicotra Giuseppe, Baldassarre Leonetta, Capellini Giovanni, Di Gaspare Luciana, Virgilio Michele, Ortolani Michele, and De Seta Monica

Subjects
heterostructures, germanium, terahertz, strong coupling, parabolic potential, Physics, QC1-999
Abstract

A parabolic potential that confines charge carriers along the growth direction of quantum wells semiconductor systems is characterized by a single resonance frequency, associated to intersubband transitions. Motivated by fascinating quantum optics applications leveraging on this property, we use the technologically relevant SiGe material system to design, grow, and characterize n-type doped parabolic quantum wells realized by continuously grading Ge-rich Si1−x Gex alloys, deposited on silicon wafers. An extensive structural analysis highlights the capability of the ultra-high-vacuum chemical vapor deposition technique here used to precisely control the quadratic confining potential and the target doping profile. The absorption spectrum, measured by means of Fourier transform infrared spectroscopy, revealed a single peak with a full width at half maximum at low and room temperature of about 2 and 5 meV, respectively, associated to degenerate intersubband transitions. The energy of the absorption resonance scales with the inverse of the well width, covering the 2.5–5 THz spectral range, and is almost independent of temperature and doping, as predicted for a parabolic confining potential. On the basis of these results, we discuss the perspective observation of THz strong light–matter coupling in this silicon compatible material system, leveraging on intersubband transitions embedded in all-semiconductor microcavities.

Published
2024
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3. Second harmonic generation in germanium quantum wells for nonlinear silicon photonics

Author

Frigerio, Jacopo, Ciano, Chiara, Kuttruff, Joel, Mancini, Andrea, Ballabio, Andrea, Chrastina, Daniel, Falcone, Virginia, De Seta, Monica, Baldassarre, Leonetta, Allerbeck, Jonas, Brida, Daniele, Zeng, Lunjie, Olsson, Eva, Virgilio, Michele, and Ortolani, Michele

Subjects
Physics - Optics, Physics - Applied Physics
Abstract

Second-harmonic generation (SHG) is a direct measure of the strength of second-order nonlinear optical effects, which also include frequency mixing and parametric oscillations. Natural and artificial materials with broken center-of-inversion symmetry in their unit cell display high SHG efficiency, however the silicon-foundry compatible group-IV semiconductors (Si, Ge) are centrosymmetric, thereby preventing full integration of second-order nonlinearity in silicon photonics platforms. Here we demonstrate strong SHG in Ge-rich quantum wells grown on Si wafers. The symmetry breaking is artificially realized with a pair of asymmetric coupled quantum wells (ACQW), in which three of the quantum-confined states are equidistant in energy, resulting in a double resonance for SHG. Laser spectroscopy experiments demonstrate a giant second-order nonlinearity at mid-infrared pump wavelengths between 9 and 12 microns. Leveraging on the strong intersubband dipoles, the nonlinear susceptibility almost reaches 10^5 pm/V, Comment: 30 pages, 6 figures, double line spacing

Published
2021

4. THz intersubband electroluminescence from n-type Ge/SiGe quantum cascade structures

Author

Stark, David, Mirza, Muhammad, Persichetti, Luca, Montanari, Michele, Markmann, Sergej, Beck, Mattias, Grange, Thomas, Birner, Stefan, Virgilio, Michele, Ciano, Chiara, Ortolani, Michele, Corley, Cedric, Capellini, Giovanni, Di Gaspare, Luciana, De Seta, Monica, Paul, Douglas J., Faist, Jérôme, and Scalari, Giacomo

Subjects
Physics - Optics, Physics - Applied Physics
Abstract

We report electroluminescence originating from L-valley transitions in n-type Ge/Si$_{0.15}$Ge$_{0.85}$ quantum cascade structures centered at 3.4 and 4.9 THz with a line broadening of $\Delta f/f \approx 0.2$. Three strain-compensated heterostructures, grown on a Si substrate by ultrahigh vacuum chemical vapor deposition, have been investigated. The design is based on a single quantum well active region employing a vertical optical transition and the observed spectral features are well described by non-equilibrium Green's function calculations. The presence of two peaks highlights a suboptimal injection in the upper state of the radiative transition. Comparison of the electroluminescence spectra with similar GaAs/AlGaAs structure yields one order of magnitude lower emission efficiency.

Published
2021
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5. Electron-hole superfluidity in strained Si/Ge type II heterojunctions

Author

Conti, Sara, Pouya, Samira Saberi, Perali, Andrea, Virgilio, Michele, Peeters, Francois M., Hamilton, Alexander R., Scappucci, Giordano, and Neilson, David

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Excitons are promising candidates for generating superfluidity and Bose-Einstein Condensation (BEC) in solid state devices, but an enabling material platform with in-built bandstructure advantages and scaling compatibility with industrial semiconductor technology is lacking. Here we predict that spatially indirect excitons in a lattice-matched strained Si/Ge bilayer embedded into a germanium-rich SiGe crystal, would lead to observable mass-imbalanced electron-hole superfluidity and BEC. Holes would be confined in a compressively strained Ge quantum well and electrons in a lattice-matched tensile strained Si quantum well. We envision a device architecture that does not require an insulating barrier at the Si/Ge interface, since this interface offers a type II band alignment. Thus the electrons and holes can be kept very close but strictly separate, strengthening the electron-hole pairing attraction while preventing fast electron-hole recombination. The band alignment also allows a one-step procedure for making independent contacts to the electron and hole layers, overcoming a significant obstacle to device fabrication. We predict superfluidity at experimentally accessible temperatures of a few Kelvin and carrier densities up to $\sim 6\times 10^{10}$ cm$^{-2}$, while the large imbalance of the electron and hole effective masses can lead to exotic superfluid phases.

Published
2020

6. Intersubband transition engineering in the conduction band of asymmetric coupled Ge/SiGe quantum wells

Author

Persichetti, Luca, Montanari, Michele, Ciano, Chiara, Di Gaspare, Luciana, Ortolani, Michele, Baldassarre, Leonetta, Zoellner, Marvin H., Mukherjee, Samik, Moutanabbir, Oussama, Capellini, Giovanni, Virgilio, Michele, and De Seta, Monica

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science, Condensed Matter - Other Condensed Matter
Abstract

: n-type Ge/SiGe asymmetric-coupled quantum wells represent the building block of a variety of nanoscale quantum devices, including recently proposed designs for a silicon-based THz quantum cascade laser. In this paper, we combine structural and spectroscopic experiments on 20-module superstructures, each featuring two Ge wells coupled through a Ge-rich tunnel barrier, as a function of the geometry parameters of the design and the P dopant concentration. Through the comparison of THz spectroscopic data with numerical calculations of intersubband optical absorption resonances, we demonstrated that it is possible to tune by design the energy and the spatial overlap of quantum confined subbands in the conduction band of the heterostructures. The high structural/interface quality of the samples and the control achieved on subband hybridization are the promising starting point towards a working electrically pumped light-emitting device.

Published
2020
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7. Room Temperature Lattice Thermal Conductivity of GeSn Alloys

Author

Concepción, Omar, primary, Tiscareño-Ramírez, Jhonny, additional, Chimienti, Ada Angela, additional, Classen, Thomas, additional, Corley-Wiciak, Agnieszka Anna, additional, Tomadin, Andrea, additional, Spirito, Davide, additional, Pisignano, Dario, additional, Graziosi, Patrizio, additional, Ikonic, Zoran, additional, Zhao, Qing Tai, additional, Grützmacher, Detlev, additional, Capellini, Giovanni, additional, Roddaro, Stefano, additional, Virgilio, Michele, additional, and Buca, Dan, additional

Published
2024
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9. The Interplay between Strain, Sn Content, and Temperature on Spatially Dependent Bandgap in Ge1−xSnx Microdisks

Author

Zaitsev, Ignatii, primary, Corley-Wiciak, Agnieszka Anna, additional, Corley-Wiciak, Cedric, additional, Zoellner, Marvin Hartwig, additional, Richter, Carsten, additional, Zatterin, Edoardo, additional, Virgilio, Michele, additional, Martín-García, Beatriz, additional, Spirito, Davide, additional, and Manganelli, Costanza Lucia, additional

Published
2024
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11. Tunability and Losses of Mid-infrared Plasmonics in Heavily Doped Germanium Thin Films

Author

Frigerio, Jacopo, Ballabio, Andrea, Isella, Giovanni, Sakat, Emilie, Biagioni, Paolo, Bollani, Monica, Napolitani, Enrico, Manganelli, Costanza, Virgilio, Michele, Grupp, Alexander, Fischer, Marco P., Brida, Daniele, Gallacher, Kevin, Paul, Douglas J., Baldassarre, Leonetta, Calvani, Paolo, Giliberti, Valeria, Nucara, Alessandro, and Ortolani, Michele

Subjects
Condensed Matter - Materials Science, Condensed Matter - Other Condensed Matter
Abstract

Heavily-doped semiconductor films are very promising for application in mid-infrared plasmonic devices because the real part of their dielectric function is negative and broadly tunable in this wavelength range. In this work we investigate heavily n-type doped germanium epilayers grown on different substrates, in-situ doped in the $10^{17}$ to $10^{19}$ cm$^{-3}$ range, by infrared spectroscopy, first principle calculations, pump-probe spectroscopy and dc transport measurements to determine the relation between plasma edge and carrier density and to quantify mid-infrared plasmon losses. We demonstrate that the unscreened plasma frequency can be tuned in the 400 - 4800 cm$^{-1}$ range and that the average electron scattering rate, dominated by scattering with optical phonons and charged impurities, increases almost linearly with frequency. We also found weak dependence of losses and tunability on the crystal defect density, on the inactivated dopant density and on the temperature down to 10 K. In films where the plasma was optically activated by pumping in the near-infrared, we found weak but significant dependence of relaxation times on the static doping level of the film. Our results suggest that plasmon decay times in the several-picosecond range can be obtained in n-type germanium thin films grown on silicon substrates hence allowing for underdamped mid-infrared plasma oscillations at room temperature., Comment: 18 pages, 10 figures

Published
2016
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12. The Interplay between Strain, Sn Content, and Temperature on Spatially Dependent Bandgap in Ge1−xSnx Microdisks

Author

Zaitsev, Ignatii, primary, Corley-Wiciak, Agnieszka Anna, additional, Corley-Wiciak, Cedric, additional, Zoellner, Marvin Hartwig, additional, Richter, Carsten, additional, Zatterin, Edoardo, additional, Virgilio, Michele, additional, Martín-García, Beatriz, additional, Spirito, Davide, additional, and Manganelli, Costanza Lucia, additional

Published
2023
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14. The Interplay between Strain, Sn Content, and Temperature on Spatially Dependent Bandgap in Ge1−xSnx Microdisks.

Author

Zaitsev, Ignatii, Corley-Wiciak, Agnieszka Anna, Corley-Wiciak, Cedric, Zoellner, Marvin Hartwig, Richter, Carsten, Zatterin, Edoardo, Virgilio, Michele, Martín-García, Beatriz, Spirito, Davide, and Manganelli, Costanza Lucia

Subjects
STRAINS & stresses (Mechanics), DEFORMATIONS (Mechanics), DEFORMATION potential, FINITE element method, METALLIC oxides, X-ray spectroscopy
Abstract

Germanium–tin (GeSn) microdisks are promising structures for complementary metal–oxide–semiconductor‐compatible lasing. Their emission properties depend on Sn concentration, strain, and operating temperature. Critically, the band structure of the alloy varies along the disk due to different lattice deformations associated with mechanical constraints. An experimental and numerical study of Ge1−xSnx microdisk with Sn concentration between 8.5 and 14 at% is reported. Combining finite element method calculations, micro‐Raman and X‐ray diffraction spectroscopy enables a comprehensive understanding of mechanical deformation, where computational predictions are experimentally validated, leading to a robust model and insight into the strain landscape. Through micro‐photoluminescence experiments, the temperature dependence of the bandgap of Ge1−xSnx is parametrized using the Varshni formula with respect to strain and Sn content. These results are the input for spatially dependent band structure calculations based on deformation potential theory. It is observed that Sn content and temperature have comparable effects on the bandgap, yielding a decrease of more than 20 meV for an increase of 1 at% or 100 K, respectively. The impact of the strain gradient is also analyzed. These findings correlate structural properties to emission wavelength and spectral width of microdisk lasers, thus demonstrating the importance of material‐related consideration on the design of optoelectronic microstructures. [ABSTRACT FROM AUTHOR]

Published
2024
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15. Nanoscale Mapping of the 3D Strain Tensor in a Germanium Quantum Well Hosting a Functional Spin Qubit Device

Author

Corley-Wiciak, Cedric, Richter, Carsten, Zoellner, Marvin H., Zaitsev, Ignatii, Manganelli, Costanza L., Zatterin, Edoardo, Schülli, Tobias U., Corley-Wiciak, Agnieszka A., Katzer, Jens, Reichmann, Felix, Klesse, Wolfgang M., Hendrickx, Nico W., Sammak, Amir, Veldhorst, Menno, Scappucci, Giordano, Virgilio, Michele, Capellini, Giovanni, Corley-Wiciak, Cedric, Richter, Carsten, Zoellner, Marvin H., Zaitsev, Ignatii, Manganelli, Costanza L., Zatterin, Edoardo, Schülli, Tobias U., Corley-Wiciak, Agnieszka A., Katzer, Jen, Reichmann, Felix, Klesse, Wolfgang M., Hendrickx, Nico W., Sammak, Amir, Veldhorst, Menno, Scappucci, Giordano, Virgilio, Michele, and Capellini, Giovanni

Subjects
silicon germanium, synchrotron, General Materials Science, thermomechanical FEM simulation, lattice strain, quantum computing, X-ray diffraction
Abstract

A strained Ge quantum well, grown on a SiGe/Si virtual substrate and hosting two electrostatically defined hole spin qubits, is nondestructively investigated by synchrotron-based scanning X-ray diffraction microscopy to determine all its Bravais lattice parameters. This allows rendering the three-dimensional spatial dependence of the six strain tensor components with a lateral resolution of approximately 50 nm. Two different spatial scales governing the strain field fluctuations in proximity of the qubits are observed at 1 μm, respectively. The short-ranged fluctuations have a typical bandwidth of 2 × 10-4 and can be quantitatively linked to the compressive stressing action of the metal electrodes defining the qubits. By finite element mechanical simulations, it is estimated that this strain fluctuation is increased up to 6 × 10-4 at cryogenic temperature. The longer-ranged fluctuations are of the 10-3 order and are associated with misfit dislocations in the plastically relaxed virtual substrate. From this, energy variations of the light and heavy-hole energy maxima of the order of several 100 μeV and 1 meV are calculated for electrodes and dislocations, respectively. These insights over material-related inhomogeneities may feed into further modeling for optimization and design of large-scale quantum processors manufactured using the mainstream Si-based microelectronics technology.

Published
2023

18. Subnanometer Control of the Heteroepitaxial Growth of Multimicrometer-Thick Ge /( Si , Ge ) Quantum Cascade Structures

Author

Talamas Simola, Enrico, primary, Montanari, Michele, additional, Corley-Wiciak, Cedric, additional, Di Gaspare, Luciana, additional, Persichetti, Luca, additional, Zöllner, Marvin H., additional, Schubert, Markus A., additional, Venanzi, Tommaso, additional, Trouche, Marina Cagnon, additional, Ortolani, Michele, additional, Mattioli, Francesco, additional, Sfuncia, Gianfranco, additional, Nicotra, Giuseppe, additional, Capellini, Giovanni, additional, Virgilio, Michele, additional, and De Seta, Monica, additional

Published
2023
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19. Germanium Quantum Wells for Non-Linear Integrated Photonics

Author

Barzaghi, Andrea, primary, Falcone, Virginia, additional, Calcaterra, Stefano, additional, Giani, Raffaele, additional, Ballabio, Andrea, additional, Isella, Giovanni, additional, Chrastina, Daniel, additional, Ortolani, Michele, additional, Virgilio, Michele, additional, and Frigerio, Jacopo, additional

Published
2022
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22. A High-Mobility Hole Bilayer in a Germanium Double Quantum Well

Author

Tosato, A. (author), Ferrari, B.M. (author), Sammak, A. (author), Hamilton, Alexander R. (author), Veldhorst, M. (author), Virgilio, Michele (author), Scappucci, G. (author), Tosato, A. (author), Ferrari, B.M. (author), Sammak, A. (author), Hamilton, Alexander R. (author), Veldhorst, M. (author), Virgilio, Michele (author), and Scappucci, G. (author)

Abstract

A hole bilayer in a strained germanium double quantum well is designed, fabricated, and studied. Magnetotransport characterization of double quantum well field-effect transistors as a function of gate voltage reveals the population of two hole channels with a high combined mobility of (Formula presented.) and a low percolation density of (Formula presented.). The individual population of the channels from the interference patterns of the Landau fan diagram was resolved. At a density of (Formula presented.) the system is in resonance and an anti-crossing of the first two bilayer subbands is observed and a symmetric-antisymmetric gap of (Formula presented.) is estimated, in agreement with Schrödinger-Poisson simulations., QCD/Scappucci Lab, QuTech, BUS/TNO STAFF, QN/Veldhorst Lab

Published
2022
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25. THz silicon photonics: an intersubband emitter

Author

Stark, David, primary, Mirza, Muhammad, additional, Persichetti, Luca, additional, Montanari, Michele, additional, Markmann, Sergej, additional, Beck, Mattias, additional, Grange, Thomas, additional, Birner, Stefan, additional, Virgilio, Michele, additional, Ciano, Chiara, additional, Ortolani, Michele, additional, Corley-Wiciak, Cedric, additional, Capellini, Giovanni, additional, Di Gaspare, Luciana, additional, De Seta, Monica, additional, Paul, Douglas J., additional, Faist, Jérôme, additional, and Scalari, Giacomo, additional

Published
2022
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26. THz electroluminescence from n-type Ge/SiGe quantum cascade structures

Author

Scalari, Giacomo, primary, Stark, David, additional, Mirza, Muhammad, additional, Persichetti, Luca, additional, Montanari, Michele, additional, Grange, Thomas, additional, Birner, Stefan, additional, Virgilio, Michele, additional, Ciano, Chiara, additional, Ortolani, Michele, additional, Corley, Cedric, additional, Capellini, Giovanni, additional, Di Gaspare, Luciana, additional, De Seta, Monica, additional, Paul, Douglas J., additional, and Faist, Jerome, additional

Published
2022
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27. Mid-infrared second harmonic generation with Ge quantum wells

Author

Frigerio, Jacopo, primary, Ciano, Chiara, additional, Ballabio, Andrea, additional, Chrastina, Daniel, additional, Allerbeck, Jonas, additional, Kuttruff, Joel, additional, Zeng, Lunjie, additional, Olsson, Eva, additional, Brida, Daniele, additional, Isella, Giovanni, additional, Virgilio, Michele, additional, and Ortolani, Michele, additional

Published
2021
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28. Second Harmonic Generation in Germanium Quantum Wells for Nonlinear Silicon Photonics

Author

Frigerio, Jacopo, primary, Ciano, Chiara, additional, Kuttruff, Joel, additional, Mancini, Andrea, additional, Ballabio, Andrea, additional, Chrastina, Daniel, additional, Falcone, Virginia, additional, De Seta, Monica, additional, Baldassarre, Leonetta, additional, Allerbeck, Jonas, additional, Brida, Daniele, additional, Zeng, Lunjie, additional, Olsson, Eva, additional, Virgilio, Michele, additional, and Ortolani, Michele, additional

Published
2021
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29. THz Intersubband Emitter based on Silicon

Author

Stark, David, primary, Mirza, Muhammad, additional, Persichetti, Luca, additional, Montanari, Michele, additional, Markmann, Sergej, additional, Beck, Mattias, additional, Grange, Thomas, additional, Birner, Stefan, additional, Virgilio, Michele, additional, Ciano, Chiara, additional, Ortolani, Michele, additional, Corley, Cedric, additional, Capellini, Giovanni, additional, Di Gaspare, Luciana, additional, De Seta, Monica, additional, Paul, Douglas J., additional, Faist, Jerome, additional, and Scalari, Giacomo, additional

Published
2021
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31. Electron–hole superfluidity in strained Si/Ge type II heterojunctions

Author

Conti, Sara (author), Saberi-Pouya, Samira (author), Perali, Andrea (author), Virgilio, Michele (author), Peeters, François M. (author), Hamilton, Alexander R. (author), Scappucci, G. (author), Neilson, David (author), Conti, Sara (author), Saberi-Pouya, Samira (author), Perali, Andrea (author), Virgilio, Michele (author), Peeters, François M. (author), Hamilton, Alexander R. (author), Scappucci, G. (author), and Neilson, David (author)

Abstract

Excitons are promising candidates for generating superfluidity and Bose–Einstein condensation (BEC) in solid-state devices, but an enabling material platform with in-built band structure advantages and scaling compatibility with industrial semiconductor technology is lacking. Here we predict that spatially indirect excitons in a lattice-matched strained Si/Ge bilayer embedded into a germanium-rich SiGe crystal would lead to observable mass-imbalanced electron–hole superfluidity and BEC. Holes would be confined in a compressively strained Ge quantum well and electrons in a lattice-matched tensile strained Si quantum well. We envision a device architecture that does not require an insulating barrier at the Si/Ge interface, since this interface offers a type II band alignment. Thus the electrons and holes can be kept very close but strictly separate, strengthening the electron–hole pairing attraction while preventing fast electron–hole recombination. The band alignment also allows a one-step procedure for making independent contacts to the electron and hole layers, overcoming a significant obstacle to device fabrication. We predict superfluidity at experimentally accessible temperatures of a few Kelvin and carrier densities up to ~6 × 1010 cm−2, while the large imbalance of the electron and hole effective masses can lead to exotic superfluid phases., QCD/Scappucci Lab, QuTech

Published
2021
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32. Terahertz intersubband electroluminescence from n-type germanium quantum wells

Author

Stark, David, primary, Mirza, Muhammad, additional, Persichetti, Luca, additional, Montanari, Michele, additional, Markmann, Sergej, additional, Beck, Mattias, additional, Grange, Thomas, additional, Birner, Stefan, additional, Virgilio, Michele, additional, Ciano, Chiara, additional, Ortolani, Michele, additional, Corley, Cedric, additional, Capellini, Giovanni, additional, Di Gaspare, Luciana, additional, De Seta, Monica, additional, Paul, Douglas J., additional, Faist, Jerome, additional, and Scalari, Giacomo, additional

Published
2021
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33. THz intersubband absorption in n-type Si1−xGex parabolic quantum wells

Author

Montanari, Michele, primary, Ciano, Chiara, additional, Persichetti, Luca, additional, Corley, Cedric, additional, Baldassarre, Leonetta, additional, Ortolani, Michele, additional, Di Gaspare, Luciana, additional, Capellini, Giovanni, additional, Stark, David, additional, Scalari, Giacomo, additional, Virgilio, Michele, additional, and De Seta, Monica, additional

Published
2021
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35. THz intersubband electroluminescence from n-type Ge/SiGe quantum cascade structures

Author

Stark, David, primary, Mirza, Muhammad, additional, Persichetti, Luca, additional, Montanari, Michele, additional, Markmann, Sergej, additional, Beck, Mattias, additional, Grange, Thomas, additional, Birner, Stefan, additional, Virgilio, Michele, additional, Ciano, Chiara, additional, Ortolani, Michele, additional, Corley, Cedric, additional, Capellini, Giovanni, additional, Di Gaspare, Luciana, additional, De Seta, Monica, additional, Paul, Douglas J., additional, Faist, Jérôme, additional, and Scalari, Giacomo, additional

Published
2021
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36. THz emission from n-type Ge/SiGe quantum cascade structures

Author

Stark, David, primary, Mirza, Muhammad, additional, Persichetti, Luca, additional, Montanari, Michele, additional, Di Gaspare, Luciana, additional, De Seta, Monica, additional, Virgilio, Michele, additional, Ortolani, Michele, additional, Capellini, Giovanni, additional, Grange, Thomas, additional, Birner, Stefan, additional, Paul, Douglas J., additional, Faist, Jérôme, additional, and Scalari, Giacomo, additional

Published
2021
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38. Design and simulation of losses in Ge/SiGe terahertz quantum cascade laser waveguides

Author

Gallacher, Kevin, Ortolani, Michele, Ciano, Chiara, Baldassarre, Leonetta, Virgilio, Michele, Scalari, Giacomo, Faist, Jérôme, Di Gaspare, Luciana, De Seta, Monica, Capellini, Giovanni, Grange, Thomas, Birner, Stefan, and Paul, Douglas J.

Abstract

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., Optics Express, 28 (4), ISSN:1094-4087

Published
2020

39. Composition analysis and transition energies of ultrathin Sn-rich GeSn quantum wells

Author

Fischer, Inga A., Clausen, Caterina J., Schwarz, Daniel, Zaumseil, Peter, Capellini, Giovanni, Virgilio, Michele, Da Silva Figueira, Maria Cecilia, Birner, Stefan, Koelling, Sebastian, Koenraad, Paul M., Huang, Michael R.S., Koch, Christoph T., Wendav, Torsten, Busch, Kurt, Schulze, Jörg, Fischer, Inga A., Clausen, Caterina J., Schwarz, Daniel, Zaumseil, Peter, Capellini, Giovanni, Virgilio, Michele, Da Silva Figueira, Maria Cecilia, Birner, Stefan, Koelling, Sebastian, Koenraad, Paul M., Huang, Michael R.S., Koch, Christoph T., Wendav, Torsten, Busch, Kurt, and Schulze, Jörg

Abstract

While GeSn alloys with high Sn content constitute direct group-IV semiconductors, their growth on Si remains challenging. The deposition of a few monolayers of pure Sn on Ge and their overgrowth with Ge using molecular beam epitaxy can be a means of obtaining Sn-rich quantum wells with very high Sn content while maintaining high crystal quality. Here, we provide structural and compositional information on such structures with very high accuracy. Based on our characterization results we theoretically predict transition energies and compare them with experimental results from photoluminescence measurements. Our results constitute the groundwork for tuning the molecular beam epitaxy based growth of Sn-rich quantum wells and dots for applications in electronic and optoelectronic devices.

Published
2020

40. Valence and conduction intersubband transitions in SiGe, Ge-rich, quantum wells on [001] [Si.sub.0.5][Ge.sub.0.5] substrates: A tight-binding approach

Author

Virgilio, Michele and Grosso, Giuseppe

Subjects
Quantum wells -- Structure, Quantum wells -- Optical properties, Silicon alloys -- Optical properties, Germanium -- Optical properties, Semiconductors -- Optical properties, Physics
Abstract

The electronic and optical properties of germanium-rich Si/SiGe quantum wells grown on [Si.sub.0.5][Ge.sub.0.5] substrates are examined by a nearest neighbor tight-binding Hamiltonian. The results for group IV conduction intersubband transitions might help in the project of devices for terahertz applications.

Published
2006

41. Theoretical investigation of near gap electronic states of Si/SiGe multiple quantum wells on (001)-Si or SiGe substrates

Author

Virgilio, Michele, Farchioni, Riccardo, and Grosso, Giuseppe

Subjects
Quantum wells -- Structure, Silicon alloys -- Atomic properties, Spin coupling -- Analysis, Germanium -- Atomic properties, Physics
Abstract

A theoretical study of the near gap electronic states of Si/Ge based multiple quantum well system composed of Si and Si (sub 1-x)Ge (sub x) alloys coherently grown on (001)-Si or SiGe substrates is presented. The calculations give an accurate description of the near gap experimental photoluminescence peaks.

Published
2006

42. The impact of donors on recombination mechanisms in heavily doped Ge/Si layers.

Author

Barget, Michael R., Virgilio, Michele, Capellini, Giovanni, Yuji Yamamoto, and Schroeder, Thomas

Subjects
*SEMICONDUCTOR doping, *GERMANIUM, *PHOTOLUMINESCENCE, *LUMINESCENCE, *CARRIER density
Abstract

Heavy n-type doping has been proposed as a route to achieve positive optical gain in germanium layers since it is supposed to enhance the Cc carrier density. Nevertheless, the impact of donor impurities on the excess carrier lifetime in heavy doped epitaxial Ge/Si layers has not yet been addressed in the literature. To elucidate this point, we investigate the optical properties of heavily doped Ge layers selectively grown on silicon by means of photoluminescence (PL) experiments and theoretical modelling. A self-consistent multi-valley effective mass numerical model for simulation of PL spectra has been implemented, taking into account the influence of dopants on the non-radiative recombination dynamics. Upon comparing measurements and modelling, we find a linear increase in the defect-related Shockley-Read-Hall (SRH) recombination rate as a function of the donor density. The non-radiative lifetime decreases from ~30 ns in intrinsic Ge/Si samples to ~0.1 ns for a doping density in the 1019 cm-3 range. As a consequence, we find that SRH is the dominant nonradiative recombination process up to a donor density of ~5 x 1019 cm-3. Despite this reduced lifetime, we observe an overall positive impact of doping on the radiative recombination rate for donor densities up to an "optimal" value of ~3 x 1019 cm-3, with a x 7 intensity enhancement compared to the intrinsic case. A further increase in the donor concentration brings about a worsening of the optical emission. [ABSTRACT FROM AUTHOR]

Published
2017
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43. N-Type Ge/SiGe Multi-Quantum Wells for THz Light Emission: High Quality Growth and Material Parameter Calibration

Author

Persichetti, Luca, primary, Ciano, Chiara, additional, Montanari, Michele, additional, Baldassarre, Leonetta, additional, Di Gaspare, Luciana, additional, Pashkin, Alexej, additional, Helm, Manfred, additional, Skibitzki, Oliver, additional, Zöllner, Marvin, additional, Capellini, Giovanni, additional, Ortolani, Michele, additional, Virgilio, Michele, additional, and De Seta, Monica, additional

Published
2020
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44. Mid-infrared second harmonic generation in Ge/SiGe coupled quantum wells

Author

Frigerio, Jacopo, primary, Ciano, Chiara, additional, Ballabio, Andrea, additional, Chrastina, Daniel, additional, Allerbeck, Jonas, additional, Kuttruff, Joel, additional, Zeng, Lunjie, additional, Olsson, Eva, additional, Brida, Daniele, additional, Isella, Giovanni, additional, Virgilio, Michele, additional, and Ortolani, Michele, additional

Published
2020
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46. Intersubband Transition Engineering in the Conduction Band of Asymmetric Coupled Ge/SiGe Quantum Wells

Author

Persichetti, Luca, primary, Montanari, Michele, additional, Ciano, Chiara, additional, Di Gaspare, Luciana, additional, Ortolani, Michele, additional, Baldassarre, Leonetta, additional, Zoellner, Marvin, additional, Mukherjee, Samik, additional, Moutanabbir, Oussama, additional, Capellini, Giovanni, additional, Virgilio, Michele, additional, and De Seta, Monica, additional

Published
2020
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47. Terahertz absorption-saturation and emission from electron-doped germanium quantum wells

Author

Ciano, Chiara, primary, Virgilio, Michele, additional, Bagolini, Luigi, additional, Baldassarre, Leonetta, additional, Pashkin, Alexej, additional, Helm, Manfred, additional, Montanari, Michele, additional, Persichetti, Luca, additional, Di Gaspare, Luciana, additional, Capellini, Giovanni, additional, Paul, Douglas J., additional, Scalari, Giacomo, additional, Faist, Jèrome, additional, De Seta, Monica, additional, and Ortolani, Michele, additional

Published
2020
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48. Composition analysis and transition energies of ultrathin Sn-rich GeSn quantum wells

Author

Fischer, Inga A., primary, Clausen, Caterina J., additional, Schwarz, Daniel, additional, Zaumseil, Peter, additional, Capellini, Giovanni, additional, Virgilio, Michele, additional, da Silva Figueira, Maria Cecilia, additional, Birner, Stefan, additional, Koelling, Sebastian, additional, Koenraad, Paul M., additional, Huang, Michael R. S., additional, Koch, Christoph T., additional, Wendav, Torsten, additional, Busch, Kurt, additional, and Schulze, Jörg, additional

Published
2020
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50. Electron Population Dynamics in Optically Pumped Asymmetric Coupled Ge/SiGe Quantum Wells: Experiment and Models

Author

Ciano, Chiara, primary, Virgilio, Michele, additional, Bagolini, Luigi, additional, Baldassarre, Leonetta, additional, Rossetti, Andrea, additional, Pashkin, Alexej, additional, Helm, Manfred, additional, Montanari, Michele, additional, Persichetti, Luca, additional, Di Gaspare, Luciana, additional, Capellini, Giovanni, additional, Paul, Douglas J., additional, Scalari, Giacomo, additional, Faist, Jèrome, additional, De Seta, Monica, additional, and Ortolani, Michele, additional

Published
2019
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