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Intersubband Transition Engineering in the Conduction Band of Asymmetric Coupled Ge/SiGe Quantum Wells
摘要： 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 SiGe tunnel barrier, as a function of the geometry parameters of the design and the P dopant concentration. Through a 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 promising starting points towards a working electrically pumped light-emitting device.
关键词： quantum wells,THz spectroscopy,group IV epitaxy,intersubband transitions,silicon–germanium heterostructures
更新于2025-09-23 15:19:57
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Spina??Controlled Nonlinear Harmonic Generations from Plasmonic Metasurfaces Coupled to Intersubband Transitions
摘要： Metasurfaces that generate nonlinear optical responses provide new degrees of freedom for applications such as nonlinear holography, wave mixing, and new frequencies generation. To extend the utility of flat nonlinear optics, metasurfaces providing both giant nonlinear response for efficient frequency mixing in subwavelength films and a single-beam output with a local wavefront control need to be developed. Metasurfaces with giant nonlinear response have recently been realized using the concept of intersubband polaritons. Separately, nonlinear metasurfaces providing a single-beam nonlinear output with a local wavefront control have been studied. However, a metasurface platform that possesses both of these properties has yet to be demonstrated. Herein, the first such platform is presented and its operation for three- and four-wave mixing processes is demonstrated. This approach is based on using Pancharatnam–Berry phase control of local nonlinear response and on employing meta-atoms with specific symmetries to enable generation of only a single nonlinear beam. Experimentally, 400 nm-thick metasurfaces with a wavefront-controlled single-beam output are demonstrated for second- and third-harmonic generation at pump wavelength of approximately 10 μm. Power conversion efficiencies of 7.6 × 10?4% and 3.6 × 10?4% are obtained for the two nonlinear processes, respectively, at peak pumping intensity of only 80 kW cm?2.
关键词： nonlinear beam-steering,nonlinear optics,spin angular momentum,metasurfaces,intersubband transitions
更新于2025-09-23 15:19:57
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Terahertz intersubband transitions in GaAsBi/AlGaAs single quantum well heterostructure
摘要： GaAsBi/AlGaAs single quantum well conduction band structure, energy levels, and their corresponding wavefunctions have been calculated by solving the Schr?dinger equation. The influences of the heterostructure parameters on the intersubband transition (ISBT) frequency within the terahertz (THz) domain have been investigated. The results show that the quantum well width has a great impact on the THz ISBT frequency. In particular, an ISBT with a frequency of 2.611 THz (10.80?meV) has been obtained for specifically optimized parameters. The study of the intersubband optical absorption coefficient (OAC) was centered in the frequency band of 2 – 14 THz ( ~ 8 – 58 meV), therefore the corresponding results are useful for the optimization of THz detectors. Correspondingly, by changing the thickness of the active layer the number of the OAC peaks has been tuned. The dipole matrix element and the Fermi occupation function have been also studied in detail. Furthermore, the influences coming from the incidence angle on the OAC intensity were numerically investigated. The obtained results could be beneficial for the design and the optimization of devices operating in the THz frequency band.
关键词： GaAsBi quantum well,Terahertz region,Intersubband transitions,Optical absorption coefficient,Incidence angle,Active layer thickness
更新于2025-09-19 17:13:59
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Electron Population Dynamics in Optically Pumped Asymmetric Coupled Ge/SiGe Quantum Wells: Experiment and Models
摘要： n-type doped Ge quantum wells with SiGe barriers represent a promising heterostructure system for the development of radiation emitters in the terahertz range such as electrically pumped quantum cascade lasers and optically pumped quantum fountain lasers. The nonpolar lattice of Ge and SiGe provides electron–phonon scattering rates that are one order of magnitude lower than polar GaAs. We have developed a self-consistent numerical energy-balance model based on a rate equation approach which includes inelastic and elastic inter- and intra-subband scattering events and takes into account a realistic two-dimensional electron gas distribution in all the subband states of the Ge/SiGe quantum wells by considering subband-dependent electronic temperatures and chemical potentials. This full-subband model is compared here to the standard discrete-energy-level model, in which the material parameters are limited to few input values (scattering rates and radiative cross sections). To provide an experimental case study, we have epitaxially grown samples consisting of two asymmetric coupled quantum wells forming a three-level system, which we optically pump with a free electron laser. The benchmark quantity selected for model testing purposes is the saturation intensity at the 1→3 intersubband transition. The numerical quantum model prediction is in reasonable agreement with the experiments and therefore outperforms the discrete-energy-level analytical model, of which the prediction of the saturation intensity is off by a factor 3.
关键词： silicon–germanium heterostructures,intersubband photoluminescence,optical pumping,intersubband transitions,electron–phonon interaction,infrared spectroscopy,quantum wells,free electron laser,terahertz quantum cascade laser
更新于2025-09-16 10:30:52
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[IEEE 2019 International Conference on Optical MEMS and Nanophotonics (OMN) - Daejeon, Korea (South) (2019.7.28-2019.8.1)] 2019 International Conference on Optical MEMS and Nanophotonics (OMN) - Hybrid Dielectric Metasurfaces: From Strong Light-Matter Interaction to Extreme Nonlinearities
摘要： We experimentally demonstrate strong coupling between Mie modes of dielectric resonators in a metasurface and intersubband transitions in semiconductor quantum wells that are embedded inside the resonator. The ability to achieve such light-matter coupling creates the possibility to realize ultrathin nonlinear optical devices that are free from complex phase matching requirements and have very high nonlinear conversion efficiencies.
关键词： Rabi splitting,Intersubband transitions,Nonlinear optics,Semiconductor heterostructures,Metasurface
更新于2025-09-16 10:30:52
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Coupled Quantum Wells
摘要： Intersubband transitions in ZnO material systems are predicted to be promising candidates for infrared and terahertz (THz) optoelectronic devices due to their unusual material properties. In particular, the temperature performance of THz quantum cascade lasers is postulated to be significantly enhanced using ZnO material systems due to their large optical phonon energy. Taking a step forward toward that goal, intersubband transitions in ZnO/MgxZn1?xO asymmetric coupled quantum wells are observed on a nonpolar m plane ZnO substrate. Two absorption peaks are observed in the energy range from approximately 250 meV to approximately 410 meV at room temperature, unambiguously demonstrating the interwell coupling in the asymmetric coupled quantum wells. A theoretical model taking into account the interaction between intersubband transitions shows reasonable overall agreement with the experimental results, thus proving the strong coupling nature of the investigated system. As the building block of complex quantum structures based on intersubband transitions, the results presented show great potential applications of ZnO/MgxZn1?xO material systems in infrared and THz optoelectronics and physics.
关键词： intersubband transitions,ZnO,optoelectronics,quantum wells,THz,infrared
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Miramar Beach, FL, USA (2019.8.19-2019.8.21)] 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Laser Level Selection in Terahertz Quantum Cascade Lasers
摘要： The active region of a terahertz quantum cascade laser with two optical transitions is studied. The population of upper laser states, which correspond to 3.4 and 3.8 THz, are investigated at different operating temperatures and in a strong magnetic field.
关键词： quantum cascade laser,terahertz,intersubband transitions
更新于2025-09-11 14:15:04
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n-type Ge/SiGe Multi Quantum-Wells for a THz Quantum Cascade Laser
摘要： Exploiting intersubband transitions in Ge/SiGe quantum cascade devices provides a way to integrate terahertz light emitters into silicon-based technology. With the view to realizing a Ge/SiGe Quantum Cascade Laser, we present the optical and structural properties of n-type strain-symmetrized Ge/SiGe asymmetric coupled quantum wells grown on Si(001) substrates by means of ultrahigh vacuum chemical vapor deposition. We demonstrate high material quality of strain-symmetrized structures and heterointerfaces as well as control over inter-well coupling and electron tunneling. Motivated by the promising results obtained on ACQWs, which are the basic building block of a cascade structure, we investigate, both experimentally and theoretically, a Ge/SiGe THz QCL design, optimized through a non-equilibrium Green’s function formalism.
关键词： Ge/SiGe,THz,intersubband transitions,strain-symmetrized,Quantum Cascade Laser
更新于2025-09-11 14:15:04
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Effect of conduction band non-parabolicity on the intersubband transitions in ZnO/Mg <sub/>x</sub> Zn <sub/>1-x</sub> O quantum well heterostructures
摘要： In this paper, we have calculated the electronic states and the coefficient of transmission in ZnO/MgxZn1-xO quantum well structures (QW), with 20% of Magnesium in both the parabolic and the non-parabolic cases. Our calculations are performed in the context of the approximation of the envelope function formalism, and using the finite difference method. The results show that the intersubband transition energy increases rapidly with well width until Lw=5nm and becomes almost constant (specially transitions E13 et E23). Wavelength λ23 decreases with well width until Lw=5nm and becomes constant. The non-parabolicity effect is more pronounced for small QW (Lw ≤ 5nm) and less marked in narrow and large QW. Also, we are studied the coefficient of transmission. We notice that when the height of barrier increases the coefficient of transmission decreases. It will be necessary to provide more energy to the electron so that it can cross the barrier. We also notice the variations related to a phenomenon of reflection quantum.
关键词： transmission coefficient,intersubband transitions,quantum well,ZnO/MgxZn1-xO,non-parabolicity
更新于2025-09-09 09:28:46