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A simulation procedure for analyzing the electrical and optical characteristics of an AlGaN/GaN intersubbandquantum well middle-wavelength infrared photodetector is presented. The photoconductive gain spectrumwas simulated by coupling the drift-diffusion and capture-escape models in the active region of the devicestructure and by ignoring the contribution of radiative emission. It was shown that the photodetector at zero biasis sensitive over a spectral range from 4 to 6 μm, with the peak absorption occurring at 4.64 μm. The dependenceof the available photocurrent on both the wavelength and the angle of incidence of an unpolarized monochromaticbeam of light was also evaluated. An assessment of the dark current characteristics was estimated at varioustemperatures.

The theoretical investigation of the electronic and nonlinear optical properties in spheroid-shaped CdTe/ZnTe core/shell quantum dots (CSQDs) embedded into two commonly adopted dielectric matrices (PVA, SiO2) is done in the framework of the Effective Mass Approximation (EMA). The discrete intra-band confined energy levels and their matching wave functions were calculated by solving the stationary Schrödinger equation taking into account the Compact Density Matrix (CDM) approach. The effect of the dielectric mismatch between the system and the capped matrix has been studied and discussed. Our numerical results revealed that the third-order nonlinear (TON) optical susceptibility χ3 is strongly influenced by the geometrical parameters and the dielectric environment.

In this work, the electronic and optical properties of CdS/ZnS core–shell quantum dots (CSQDs) capped in different matrices were investigated theoretically. Through the effective mass approximation (EMA) and the density matrix approach (DMA), the quantized energy levels and their corresponding wave functions of the system were obtained by solving the Schrödinger equation in a spherical coordinates system. In addition, the effects of the incident optical intensity, the number of dots per unit volume, dielectric mismatch of the organic and inorganic matrix, and geometric parameters of the structure, such as the core/shell radius ratio for CdS/ZnS CSQDs on the optical properties, were evaluated and discussed. The results revealed that both the size and dielectric environments had a substantial effect on the optical features of these nanostructures. [ABSTRACT FROM AUTHOR]

In this study, we report on the ultra-short lifetime of excited intersubband electrons in a 38 Å wide AlGaN/GaN-based quantum well. The rapid decay of these charge carriers occurs due to a resonance between the relevant intersubband transition energy and the size of the GaN-based LO-phonon at 92 meV. Based on the experimentally observed Lorentz-shaped intersubband emission peak with a spectral width of roughly 6 meV (48 cm−1) respecting the Fourier transform limit, a very short lifetime, namely 111 fs, could be calculated. By comparing this lifetime to the existing literature data, our value confirms the potential high-speed capability of III-nitride-based optoelectronics. [ABSTRACT FROM AUTHOR]

In this work, we perform a theoretical analysis of the electronic and optical properties of CdS quantum dot (QD) encapsulated in ZnSe matrix. The intersubband energy levels and the matching wave functions are calculated using the effective mass approximation (E.M.A) and the compact density matrix approach. The effect of self-energy contribution due to the charging of CdS QD with ZnSe matrix has been taken into account from the beginning. We found that the linear and nonlinear optical properties are considerably impacted by the size parameter and the optical intensity I. The results obtained have essential consequences for the design of optoelectronic and photonic devices. [ABSTRACT FROM AUTHOR]

Using the matrix diagonalization method within the effective mass approximation and the rectangular potential profile, we investigate optical absorption coefficients (OAC) in the core-shell quantum antidot (QAD) Al0.3Ga0.7 As/GaAs/Al0.3Ga0.7 As in the presence of applied co-directed electrical and magnetic fields. The electric field effect on the electron wave functions, energy spectrum, oscillator strength of the intersubband electronic transitions is calculated for different size of QAD core and different value of the magnetic field induction. The total, linear and nonlinear optical absorption coefficients in QAD are obtained by considering 1 s-1p and 1p-1d electron quantum transitions as functions of the incident photon energy. [ABSTRACT FROM AUTHOR]

The electronic quasi-bound state in the continuum concept is explored in an InGaAs/InAlAs heterostructure to create a voltage-tunable dual-colour quantum Bragg mirror detector. This heterostructure is based on one main quantum well embedded between two different superlattices. By bandgap engineering, each superlattice gives rise to quasi-bound states in the continuum with a preferential direction for electron extraction. Due to these states, the photovoltaic photocurrent presents a dual-colour response, one in a positive direction at 340 meV (3.6 μm), and one in a negative direction at 430 meV (2.9 μm). The simultaneous dual-colour detection can be switched to a single-colour detection (340 meV or 430 meV) by applying a bias voltage. At 77 K, the specific detectivity for simultaneous dual-colour is 2.5·108 Jones, while the single-colour detectivities are 2.6·109 Jones at +2.0 V and 7.7·108 Jones at -1.6 V for 340 meV and 430 meV, respectively. [ABSTRACT FROM AUTHOR]

In this study, we report on the ultra-short lifetime of excited intersubband electrons in a 38 Å wide AlGaN/GaN-based quantum well. The rapid decay of these charge carriers occurs due to a resonance between the relevant intersubband transition energy and the size of the GaN-based LO-phonon at 92 meV. Based on the experimentally observed Lorentz-shaped intersubband emission peak with a spectral width of roughly 6 meV (48 cm−1) respecting the Fourier transform limit, a very short lifetime, namely 111 fs, could be calculated. By comparing this lifetime to the existing literature data, our value confirms the potential high-speed capability of III-nitride-based optoelectronics.

Intersubband transition was recently discovered in colloidal nanoplatelets, but the associated intersubband carrier relaxation dynamics remains poorly understood. In particular, it is crucial to selectively excite the intersubband transition and to follow the hot electron dynamics in the absence of valence-band holes. This is achieved herein by exciting the predoped electrons in CdSe/ZnS nanoplatelets using near-infrared femtosecond pulses and monitoring nonequilibrium electron dynamics using broad-band visible pulses. We find that the n = 2 electrons relax to the n = 1 subband and establish a Fermi-Dirac distribution within 200 fs, and finally reach an equilibrium with the lattice within a few ps. The cooling dynamics depend mainly on the excitation fluence but weakly on the doping density and the lattice temperature. These characteristics are well captured by our numerical simulation that explicitly accounts for the state occupation effect and optical phonon scattering.

• Intersubband transition in CdTe/ZnTe core/shell prolate spheroidal QDs. • Nonlinear third-order optical susceptibility is investigated with eccentricity e 1. • Nonlinear third-order optical susceptibility is shifted with surrounding polymer matrix. The theoretical investigation of the electronic and nonlinear optical properties in spheroid-shaped CdTe/ZnTe core/shell quantum dots (CSQDs) embedded into two commonly adopted dielectric matrices (PVA, SiO 2) is done in the framework of the Effective Mass Approximation (EMA). The discrete intra-band confined energy levels and their matching wave functions were calculated by solving the stationary Schrödinger equation taking into account the Compact Density Matrix (CDM) approach. The effect of the dielectric mismatch between the system and the capped matrix has been studied and discussed. Our numerical results revealed that the third-order nonlinear (TON) optical susceptibility χ 3 is strongly influenced by the geometrical parameters and the dielectric environment. [ABSTRACT FROM AUTHOR]

Strong and ultrastrong coupling between intersubband transitions in quantum wells and cavity photons have been realized in mid-infrared and terahertz spectral regions. However, most previous works employed a large number of quantum wells on rigid substrates to achieve coupling strengths reaching the strong or ultrastrong coupling regime. In this work, we experimentally demonstrate ultrastrong coupling between the intersubband transition in a single quantum well and the resonant mode of photonic nanocavity at room temperature. We also observe strong coupling between the nanocavity resonance and the second-order intersubband transition in a single quantum well. Furthermore, we implement for the first time such intersubband cavity polariton systems on soft and flexible substrates and demonstrate that bending of the single quantum well does not significantly affect the characteristics of the cavity polaritons. This work paves the way to broaden the range of potential applications of intersubband cavity polaritons including soft and wearable photonics.

The concept of strong light-matter coupling has been demonstrated in semiconductor structures, and it is poised to revolutionize the design and implementation of components, including solid state lasers and detectors. We demonstrate an original nanospectroscopy technique that permits the study of the light-matter interaction in single subwavelength-sized nanocavities where far-field spectroscopy is not possible using conventional techniques. We inserted a thin (∼150 nm) polymer layer with negligible absorption in the mid-infrared range (5 μm < λ < 12 μm) inside a metal-insulator-metal resonant cavity, where a photonic mode and the intersubband transition of a semiconductor quantum well are strongly coupled. The intersubband transition peaks at λ = 8.3 μm, and the nanocavity is overall 270 nm thick. Acting as a nonperturbative transducer, the polymer layer introduces only a limited alteration of the optical response while allowing to reveal the optical power absorbed inside the concealed cavity. Spectroscopy of the cavity losses is enabled by the polymer thermal expansion due to heat dissipation in the active part of the cavity, and performed using atomic force microscopy (AFM). This innovative approach allows the typical anticrossing characteristic of the polaritonic dispersion to be identified in the cavity loss spectra at the single nanoresonator level. Results also suggest that near-field coupling of the external drive field to the top metal patch mediated by a metal-coated AFM probe tip is possible, and it enables the near-field mapping of the cavity mode symmetry including in the presence of a strong light-matter interaction.

Piezo-phototronic effect on intersubband transition of valence band is studied by the hybrid kp theory tight-binding model approach. Piezoelectric properties of multilayer MoS 2 show the layer-dependent behaviors, which offer new way to design quantum well by strain induced polarization. In this work, we design a kind of van der Waals quantum well based on multilayer MoS 2. The intersubband transition energy can be regulated within terahertz by strain. The transition strength is studied by calculating oscillator strength. The novel structures not only offer a new degree of freedom for piezotronic and piezo-phototronic materials and devices, but also pave a new way to design optoelectronic nanoscale devices. A layer-dependent van der Waals quantum well based on few-layer MoS 2 is proposed for terahertz optoelectronic devices. Piezotronic and piezo-phototronic van der Waals crystals are good platforms for strain manipulation and layer-by-layer materials design due to fine-tune fabrication of hetero-structures. [Display omitted] • Strain-induced piezoelectric field can effectively modulate intersubband transition of quantum well. • The intersubband transition energy of valence is in terahertz range. • Piezotronic and piezo-phototronic van der Waals crystals are good platforms for strain manipulation. [ABSTRACT FROM AUTHOR]