Semiconductor Quantum-well Structures Research Articles

Identification of electronic dimensionality reduction in semiconductor quantum well structures

Two-dimensional (2D) systems, such as high-temperature superconductors, surface states of topological insulators, and layered materials, have been intensively studied using vacuum-ultraviolet (VUV) angle-resolved photoemission spectroscopy (ARPES). In semiconductor films (heterostructures), quantum well (QW) states arise due to electron/hole accumulations at the surface (interface). The quantized states due to quantum confinement can be observed by VUV-ARPES, while the periodic intensity modulations along the surface normal (kz) direction of these quantized states are also observable by varying incident photon energy, resembling three-dimensional (3D) band dispersion. We have conducted soft X-ray (SX) ARPES measurements on thick and ultrathin III-V semiconductor InSb(001) films to investigate the electronic dimensionality reduction in semiconductor QWs. In addition to the dissipation of the kz dispersion, the SX-ARPES observations demonstrate the changes of the symmetry and periodicity of the Brillouin zone in the ultrathin film as 2D QW compared with these of the 3D bulk one, indicating the electronic dimensionality reduction of the 3D bulk band dispersion caused by the quantum confinement. The results provide a critical diagnosis using SX-ARPES for the dimensionality reduction in semiconductor QW structures.

Nonlinear parametric generation in a four-level inverted-type quantum well nanostructure

In this study, we introduce an innovative semiconductor quantum well (SQW) nanostructure, which exhibits a unique four-level configuration arranged in an inverted Y-shape. This configuration enables interaction with three laser fields and demonstrates the intriguing nonlinear phenomenon of parametric generation. Our investigation delves into a wide range of parametric conditions, aiming to understand the profound impact of various system parameters on the generation and propagation of new light fields within this groundbreaking nanostructure. By employing a combination of analytical and numerical methods, we not only reveal the potential for precise manipulation of coherence among energy levels but also showcase its practical implications — high-efficiency and tunability in the parametric generation process. This pioneering scheme represents a significant advancement in the field of SQW structures, bridging the gap between theoretical exploration and practical application. Our findings promise exciting prospects for the development of novel light sources and optical devices based on SQW structures, thereby pushing the boundaries of what is achievable in various applications and setting new standards for the state-of-the-art in this domain.

TUNNEL BROADENING OF RESONANT LEVELS IN LAYERED QUANTUM-SIZE STRUCTURES

The microparticles interaction with potential barriers of various nature and form is the quantum physics and nanoelectronics basis. The nature of this interaction largely determines modern radio engineering devices and complexes operation, information transmission and processing systems. At present, semiconductor quantum-well structures, in particular heterostructures with quantum wells (QWs) and barriers (QWs), occupy leading positions as materials for opto- and nanoelectronics. It has been found that chain consisting of a sequence formation of potential wells and barriers gives rise to resonant levels for which the structure transparency is equal to unity. With an increase in the number of chain links, these levels split into close sublevels, the energy and half-width of which depend on the barriers parameters and the number of chain cells. A technique is proposed to determine the characteristics of these levels, in particular, the half-width of sublevels. The wave function dependence on chain parameters is studied. Problems related to the propagation of waves in layered media also arise in many other branches of science and technology. In particular, such media as plasma, ionosphere, atmosphere, ocean contain layered structures. Solving the problems of wave propagation in these media, calculating the reflection and transmission coefficients during the propagation of electromagnetic waves are of great importance both for calculating radio paths with reflection from the ionosphere and for many problems of remote diagnostics of ionospheric plasma. The issues discussed in this paper may be of interest to specialists in these areas.

Electrorefraction beyond the excitonic resonance in GaAs/AlGaAs multiple quantum well structure in the Franz-Keldysh geometry

The Kramers-Kronig relations were used to estimate electrorefractivity near the edge of the exciton absorption peak of GaAs/AlGaAs photorefractive quantum well (PMQW) structure working in the Franz-Keldysh geometry. It was shown that for both TE and TM polarizations the change of the refractive index under an applied electric field is at least an order of magnitude greater than in bulk semi-insulating GaAs due to the classical Franz-Keldysh effect. Full Text: PDF ReferencesD.D. Nolte, M. R. Melloch in: Photorefractive effects and Materials, ed. by D. D. Nolte (Kluwer, Dordrecht 1995). CrossRef T. E.Van Eck, L. M. Walpita, W.S.C. Chang, H. H. Wieder, "Franz–Keldysh electrorefraction and electroabsorption in bulk InP and GaAs", Appl. Phys. Lett. 48, 451 (1986). CrossRef P.K. Basu, Theory of Optical Processes in Semiconductors, (Oxford University Press, 2003) ch. 7. CrossRef A Partovi. E.M. Garmire, "Band‐edge photorefractivity in semiconductors: Theory and experiment", J. Appl. Phys. 69, 6885 (1991). CrossRef J. S. Weiner, D. A. B. Miller, D. S. Chemla, et. al. "Strong polarization‐sensitive electroabsorption in GaAs/AlGaAs quantum well waveguides", Appl. Phys. Lett. 47, 1148 (1985). CrossRef D. S. Chemla, D. A. B. Miller, "Room-temperature excitonic nonlinear-optical effects in semiconductor quantum-well structures", JOSA A, 2 1155, (1985). CrossRef S.L. Chuang, Physics of Photonic Devices (2-nd ed. New Jersey, Wiley & Sons 2009), ch. 14. DirectLink E. Miśkiewicz, A. Ziółkowski, M. Wichtowski, E. Weinert - Rączka, "Thermally induced changes of the electro-optical properties of semi-insulating GaAs/AlGaAs multiple quantum well structures", Opt. Mat. 89, 231 (2019). CrossRef E.Weinert-Rączka, R.Iwanow, "Asymetric directional coupler controlled by photorefractive grating", Acta Phys. Pol. A 95, 813 (1999). CrossRef

Molecular engineering of organic-inorganic hybrid perovskites quantum wells.

Semiconductor quantum-well structures and superlattices are key building blocks in modern optoelectronics, but it is difficult to simultaneously realize defect-free epitaxial growth while fine tuning the chemical composition, layer thickness and band structure of each layer to achieve the desired performance. Here we demonstrate the modulation of the electronic structure-and consequently the optical properties-of organic semiconducting building blocks that are incorporated between the layers of perovskites through a facile solution processing step. Self-aggregation of the conjugated organic molecules is suppressed by functionalization with sterically demanding groups and single crystalline organic-perovskite hybrid quantum wells (down to one-unit-cell thick) are obtained. The energy and charge transfers between adjacent organic and inorganic layers are shown to be fast and efficient, owing to the atomically flat interface and ultrasmall interlayer distance of the perovskite materials. The resulting two-dimensional hybrid perovskites are very stable due to protection given by the bulky hydrophobic organic groups.

Atomically-Thin CdSe and CdTe Colloidal Nanosheets: Growth, Crystal Structure, and Optical Properties

The article describes the main features of a new class of colloidal nanoparticles with the electronic structure of semiconductor quantum wells – atomically-thin cadmium selinide CdSe and cadmium telluride CdTe nanosheets with a thickness of 1-2 nm and extended lateral sizes in the range of 100–700 nm. Approaches to the synthesis of such nanostructures by wet chemical methods are considered. A new effect of spontaneous folding induced by ligand exchange has been described.

A new coupling mechanism between two graphene electron waveguides for ultrafast switching

In this paper, we report a novel coupling between two graphene electron waveguides, in analogy the optical waveguides. The design is based on the coherent quantum mechanical tunneling of Rabi oscillation between the two graphene electron waveguides. Based on this coupling mechanism, we propose that it can be used as an ultrafast electronic switching device. Based on a modified coupled mode theory, we construct a theoretical model to analyze the device characteristics, and predict that the switching speed is faster than 1 ps and the on–off ratio exceeds 106. Due to the long mean free path of electrons in graphene at room temperature, the proposed design avoids the limitation of low temperature operation required in the traditional design by using semiconductor quantum-well structure. The layout of our design is similar to that of a standard complementary metal-oxide-semiconductor transistor that should be readily fabricated with current state-of-art nanotechnology.

(2 + 1)-D spatial ring solitons in a semiconductor quantum well system

In this paper, we investigate the interaction between the semiconductor quantum well (QW) structure, a weak probe field and a strong control field. Due to the quantum interference effect induced by the strong control field, the absorption of the weak probe field is small and the Kerr nonlinearity can be greatly enhanced. The results show that the spatial soliton can form in the semiconductor QW structure via electromagnetically induced transparency (EIT). We also discuss the optical response of the system and obtain the giant χ(3) and χ(5) susceptibilities with opposite signs. In the one-dimension case, we obtain the analytical solutions for bright and dark spatial solitons. For a general case, we present numerical solutions for ring solitons with experimental parameters and show that the ring solitons are stable against azimuthal perturbation.

Interference Effects on Optical Spectra of Mahan Exciton in Semiconductor Quantum Wells

Optical absorption spectra of modulation-doped n-type semiconductor quantum-well structures are studied theoretically. It is shown that effective Coulomb interaction of a photo-excited hole with the sea of electrons in n=1 conduction-subband via 2D hydrogenic exciton states associated with the unoccupied higher subbands yields an appearance of new subband interference structure on the continuous tail of the Mahan exciton. Numerical results with use of material parameters for GaAs exhibit clearly such effects on the calculated absorption spectra.

Theory of non-polar and semi-polar nitride semiconductor quantum-well structures

We investigate the electronic and optical properties of non-polar a- and m-planes and semi-polar InGaN–GaN quantum-well structures using the multiband effective-mass theory taking into account the many-body effects. These results are compared with those of (0 0 0 1) oriented c-plane wurtzite InGaN–GaN quantum wells. We derive explicitly the valence-band Hamiltonian and interband optical matrix elements with polarization dependence for an arbitrary crystal polar angle θ and an azimuthal angle φ. The average hole effective masses of the topmost valence band along the wave vector perpendicular to the crystal orientation for the non-polar and semi-polar cases are substantially lower than that of the c-plane case. It is found that the azimuthal angle φ does not change the shape of the band structure but shifts the sub-band position. Thus the transition energy will be dependent on both the polar angle θ and the azimuthal angle φ. It is expected that the optical matrix elements are strongly anisotropic and optical gain would be larger for the non-polar and semi-polar cases because of the vanishing of the internal electric fields.

Pump-probe optical response and four-wave mixing in intersubband transitions of a semiconductor quantum well

We study theoretically the absorption and dispersion of a probe field in the presence of a near-resonant pump field and the four-wave mixing in intersubband transitions of a semiconductor quantum-well structure. We take into account the effects of electron-electron interactions and consider the interaction of the two-subband system with rectangular electromagnetic fields. For the description of the system dynamics we use the effective nonlinear Bloch equations, which due to the effects of electron-electron interactions contain renormalized terms for the transition energy and the applied field. We combine these equations and write the proper differential equations of the density matrix elements for the several nonlinear optical processes, under the rotating wave approximation. These equations are solved analytically, in the steady state, for a GaAs/AlGaAs quantum-well structure. We show that the probe absorption and dispersion and the four-wave mixing spectra of a strongly driven two-subband system can be significantly dependent on the frequency and the intensity of the pump field and on electron sheet density. Specifically, we have found that the absorption, dispersion and the four-wave mixing spectra are practically independent of the electron sheet density in the case that the pump field is on resonance, and in the case for a rather strong pump field independently of its detuning. In the case of moderate intensity and off-resonant pump fields the influence of the electron-electron interactions on the reported spectra is more eminent for positive detuning of the pump field.

Ultrafast partial measurement of fourth-order coherence by HBT interferometry of upconversion-based autocorrelation

We introduce, analyze, and experimentally demonstrate a compact semiconductor-based scheme for a femtosecond-scale partial fourth-order coherence g((4)) measurements. The scheme is based on a start-stop photon-counting Hanbury Brown and Twiss (HBT) interferometry of an upconversion-based Michelson-interferometer autocorrelation. The experimental realization employs second-harmonic generation in a semiconductor quantum-well structure, which may be further integrated with the HBT setup as a miniature photonic circuit, allowing compact characterization devices for photon-pair statistics in quantum photonics and quantum information processing.

Electrically Induced Two-Photon Transparency in Semiconductor Quantum Wells

We demonstrate experimentally two-photon transparency, achieved by current injection into a semiconductor quantum-well structure which exhibits two-photon emission. The two-photon induced luminescence is progressively reduced by the injected current, reaching the point of two-photon transparency-a necessary condition for semiconductor two-photon gain and lasing. These results agree with our calculations.

Excitation density distribution in electron-beam-pumped ZnSe semiconductor lasers

The spatial density distribution of the absorbed energy in ZnSe semiconductor lasers excited by electrons with energies from 2 keV to 1 MeV is calculated by the Monte-Carlo method. Approximate analytic expressions determining the absorbed energy of electrons in ZnSe are presented. The pump power threshold in a semiconductor quantum-well ZnSe structure is experimentally determined. The lasing threshold in such structures is estimated as a function of the electron energy.

Berry Phase Effect on the Exciton Transport and on the Exciton Bose-Einstein Condensate

With the exciton lifetime much extended in semiconductor quantum-well structures, the exciton transport and Bose-Einstein condensation have become a focus of research in recent years. We reveal a momentum-space gauge field in the exciton center-of-mass dynamics due to Berry phase effects. We predict a spin-dependent transport of the excitons analogous to the anomalous Hall and Nernst effects for electrons. We also predict spin-dependent circulation of a trapped exciton gas and instability in an exciton condensate in favor of vortex formation.

Semiconductor saturable absorbers with recovery time controlled by lattice mismatch and band-gap engineering

The recovery time of absorption in semiconductor quantum-well structures is one of the key parameters that determines the performance of pulsed lasers mode-locked or Q-switched by semiconductor saturable absorbers. In this paper we discuss new methods to control the recovery time of absorption. The first method is based on controlling the crystalline quality of the absorbing material and thus the density of non-radiative recombination centers that are responsible for the fast recovery of the absorption. With this technique, we were able to fabricate semiconductor saturable absorber mirrors (SESAMs) with recovery times of about 4.5 ps at 1 μm and 40 ps at 1.55 μm. Another approach that we propose and demonstrate in this paper is based on band-gap engineering that enables short recovery times to be achieved through fast relaxation of excited photocarriers via intraband scattering. A 24 ps carrier decay time was achieved by placing deep quantum-wells next to the shallow quantum-wells responsible for the nonlinear absorption. We demonstrated that the recovery time can be changed by modifying the thickness of the deep and shallow quantum-wells.

Erratum: Signatures of Discontinuity in the Exchange-Correlation Energy Functional Derived from the Subband Electronic Structure of Semiconductor Quantum Wells [Phys. Rev. Lett.98, 066806 (2007)

The discontinuous character of the exact exchange-correlation $(xc)$ energy functional of Density Functional Theory is shown to arise naturally in the subband spectra of semiconductor quantum wells. Using an \emph{ab-initio} $xc$ functional, including exchange exactly and correlation in an exact partial way, a discontinuity appears in the $xc$ potential, each time a subband becomes slightly occupied. Exchange and correlation give opposite contributions to the discontinuity, with correlation overcoming exchange. The jump in the intersubband energy is in excellent agreement with experimental data.

EDGE MAGNETOPLASMONS FOR A NEW TYPE OF QUANTUM-WELL MICROWAVE DETECTOR

We theoretically study the wavelength and the propagation length of the edge magnetoplasmons (EMP's), running along the edge of a two-dimensional (2D) electron layer in a semiconductor quantum-well structure with and without metallic gates. We show that the metallic gate suppresses the propagation of the EMP's, but the quality factor of the wave (q′/q″, where q′ and q″ are the real and imaginary parts of the complex EMP wavevector) can be larger in the gated structures as compared to the structures without the gate. The results may be useful for analysis of operation of the recently discovered microwave detectors and spectrometers operating at liquid nitrogen temperatures (Kukushkin et al., Appl. Phys. Lett. 86, 044101 (2005)).

Signatures of Discontinuity in the Exchange-Correlation Energy Functional Derived from the Subband Electronic Structure of Semiconductor Quantum Wells

The discontinuous character of the exact-exchange-correlation (xc) energy functional of density functional theory is shown to arise naturally in the subband spectra of semiconductor quantum wells. Using an ab initio xc functional, including exchange exactly and correlation in an exact partial way, a discontinuity appears in the xc potential, each time a subband becomes slightly occupied. Exchange and correlation give opposite contributions to the discontinuity, with correlation overcoming exchange. The jump in the intersubband energy is in excellent agreement with experimental data.

Propagation of edge magnetoplasmons in semiconductor quantum-well structures

The wavelength and the propagation length of the edge magnetoplasmons, running along the edge of a two-dimensional electron layer in a semiconductor quantum-well structure, are theoretically studied as a function of frequency, magnetic field, electron density, mobility, and geometry of the structure. The results are intended to be used for analysis and optimization of operation of recently invented quantum-well microwave spectrometers operating at liquid-nitrogen temperatures [I. V. Kukushkin et al., Appl. Phys. Lett. 86, 044101 (2005)].