Interband Light Research Articles

The Influence of Polarized Phonons on Interband Light Absorption in Spheroidal Quantum Dots of the CdS/SiO2 Heterosystem

The influence of confined phonons on the coefficient of interband absorption of polarized light as a function of its frequency has been investigated. A comparison was made between the obtained results and those obtained considering polarized phonons in a bulk crystal. The dependence of interband light absorption on the ellipsoid's axis ratio has been established. Calculations were performed for various temperatures and radii of the quantum dot in the CdS/SiO2 heterostructure, shaped as an elongated spheroid.

Optical Properties of Conical Quantum Dot: Exciton-Related Raman Scattering, Interband Absorption and Photoluminescence.

The current work used the effective mass approximation conjoined with the finite element method to study the exciton states in a conical GaAs quantum dot. In particular, the dependence of the exciton energy on the geometrical parameters of a conical quantum dot has been studied. Once the one-particle eigenvalue equations have been solved, both for electrons and holes, the available information on energies and wave functions is used as input to calculate exciton energy and the effective band gap of the system. The lifetime of an exciton in a conical quantum dot has been estimated and shown to be in the range of nanoseconds. In addition, exciton-related Raman scattering, interband light absorption and photoluminescence in conical GaAs quantum dots have been calculated. It has been shown that with a decrease in the size of the quantum dot, the absorption peak has a blue shift, which is more pronounced for quantum dots of smaller sizes. Furthermore, the interband optical absorption and photoluminescence spectra have been revealed for different sizes of GaAs quantum dot.

Multi-zone resonance spectrometry of inelastic electron scattering of light and the manifestation of strong spin-orbit interaction in nanostructures with quantum dots

Highly sensitive methods of inelastic light scattering spectrometry have been developed to detect individual photons in the visible and near-infrared spectral ranges (0.4-1.35) μm. Precision optical measurements of vibrational and electronic states of nanostructures with quantum objects are performed, using the example of quantum-dimensional nanoheterostructures (311)In si-GaAs/InAs with InAs quantum dots. A distinctive attractive feature of such structures with a degenerate valence band of symmetry 8 is the presence of a strong spin-orbit interaction. In this case, the intrinsic moment of the holes can effectively interact with the electric field of the incident light wave. It was found that such interaction causes intense luminescence and inelastic scattering of the light wave in the IR region of the 0.9-1.35 μm spectrum. Effective generation of nonequilibrium electron-hole (e-h) plasma with concentrations n=p=1.0·1017 cm-3 and T_e=T_h=25 K,was revealed under resonant excitation conditions, while the lattice temperature T_L=5.1 K. New mechanisms have been discovered for the formation of an abnormally intense integration spectrum of multiplex inelastic light scattering of a rather complex shape formed by various separable resonant contributions of the processes of quasi-elastic scattering by charge carriers, light scattering by acoustic plasmons of electron-hole plasma, as well as inelastic intra- and inter-band light scattering by heavy holes. It has been established that the anomalous intensity gain of such multi-zone selective resonant light scattering is more than 105 times higher than the intensity of Thomson light scattering on individual charge carriers. There is agreement between the estimated calculated and experimental spectra, and for the most part for the difficult-to-interpret significant width of the observed light scattering line. It is shown that new mechanisms of various contributions to the formation of scattered photon radiation are important diagnostic elements that are clearly manifested in the spectra of the resulting enhanced inelastic light scattering. Keywords: nanostructures, quantum objects, resonant scattering of light by charge carriers, exchange interaction, plasma diagnostics.

Analytical study of absorption threshold frequency of tuned quantum dot/ring system

In the present work, a tuned quantum dot/ring system under an external magnetic field is studied. Analytical methods are used to derive the wave functions and energy eigenvalues. The interband light absorption coefficient is then calculated analytically. Additionally, an analytical relationship is derived for the absorption threshold frequency (ATF) of the system. It is observed using those analytical formulas that: i) The ATF behaves differently for large and small magnetic fields. ii) The ATF increases as the magnetic field is increased and decreases as system size is increased. iii) The ATF can be increased by enhancing the repulsive potential of the system. Our results show that the model can be transformed into either a 2D quantum disk or ring, offering the possibility of using our findings about the absorption coefficient and ATF in photodetectors based on 2D quantum dots.

Density of states and interband light absorption in Y2O3 and Sc2O3 thin films

The long-wavelength edge of the fundamental absorption band of thin Y2O3 and Sc2O3 films obtained by the method of discrete evaporation in vacuum is investigated. On the basis of its temperature dependence, the excitons - phonon interaction is investigated, which made it possible to interpret the absorption edge as the absorption of self-trapped excitons. To analyze the experimental results, we used a model of a heavily doped or defective semiconductor in the quasi-classical approximation. The use of this model made it possible to estimate the radius of the ground electronic state a and the screening radius rS and the concentration of free charge carriers N in the films under study.

Influence of the Composition of the Radio-Frequency Sputtering Atmosphere on the Density of States and Interband Light Absorption in thin Y2O3 Films

Influence of the Composition of the Radio-Frequency Sputtering Atmosphere on the Density of States and Interband Light Absorption in thin Y2O3 Films

Density of States and Interband Light Absorption in β-Ga2O3 Thin Films

Density of States and Interband Light Absorption in β-Ga2O3 Thin Films

Interband Light Absorption in a Superlattice Consisting of Alternating Segments of Single and Double Layers of Graphene

A model of a superlattice consisting of alternating single and double layers of graphene is studied. The energy spectrum of the superlattice can be controlled by an external electric field perpendicular to a sample’s surface. It is shown that the energy spectrum of such a structure can be approximated by the Kane model. The coefficient of interband absorption for such a superlattice is calculated.

Anomalous electron polarizability of HgTe quantum wells

The polarizability of electrons in CdTe/Cd x Hg 1− x Te/CdTe quantum wells is studied. It is shown that polarizability in the quantum well without cadmium is negative, i.e., the displacement of an electron and hole in the main subbands of spatial quantization in an electric field applied perpendicularly to the quantum well plane is opposite to the force acting on it. It is predicted that the negative polarizability can reduce the dielectric constant of quantum wells by up to 15% and manifest itself as the blue shift of the interband light absorption edge in an electric field.

Vertical cavity surface emitting laser of 1.55 μm spectral range, manufactured by molecular beam epitaxy and wafer fusion technique

The heterostructure design for 1.55 μm range VCSELs is proposed and realized. The wafer fusion technique was used to form the final heterostructure. The growth of AlGaAs/GaAs distributed Bragg reflectors (DBRs) on GaAs substrate and the optical cavity with an active region on InP substrate as well as a tunnel junction (TJ) regrowth was performed by molecular beam epitaxy (MBE). A key feature of the proposed design is the use of n++-InGaAs/p++-InGaAs/p++-InAlGaAs TJ, which allows, due to the effective removal of oxide from the InGaAs surface, to use MBE for re-growth of the TJ surface relief. Despite of the presence in heterostructure a narrow-gap InGaAs layers, a noticeable increase in internal optical loss in lasers can be avoided due to the short-wavelength shift of the edge of interband light absorption in ++-InGaAs layers (Burshtein-Moss effect). Fabricated VCSELs demonstrate single-mode operation with a threshold current less than 2 mA and a slope efficiency of ~ 0.46 W/A, which are comparable with characteristics of VCSELs with n++/p++-InAlGaAs TJ with a similar level of mirror losses.

Electronic and Optical Properties of RCuGe Compounds (R = Dy, Ho)

Results are presented from investigating the electronic structure and optical properties of DyCuGe and HoCuGe compounds. Spin-polarized calculations of the band structure are made using the local spin density approximation that allows for strong electronic correlations in the 4f-shells of rare earth ions. The optical properties of these alloys are studied in a broad range of wavelengths via ellipsometry. The calculated electron densities of states are used to interpret the experimental energy dependences of optical conductivities in the region of interband light absorption.

Effect of Electronic Correlations on the Electronic Structure, Magnetic and Optical Properties of the Ternary RCuGe Compounds with R = Tb, Dy, Ho, Er.

In this study, the ab initio and experimental results for RCuGe ternary intermetallics were reported for R = Tb, Dy, Ho, Er. Our theoretical calculations of the electronic structure, employing local spin density approximation accounting for electron–electron correlations in the 4f shell of Tb, Dy, Ho, Er ions were carried in DFT+U method. The optical properties of the RCuGe ternary compounds were studied at a broad range of wavelengths. The spectral and electronic characteristics were obtained. The theoretical electron densities of states were taken to interpret the experimental energy dependencies of the experimental optical conductivity in the interband light–absorption region. From the band calculations, the 4f shell of the rare-earth ions was shown to provide the major contribution to the electronic structure, magnetic and optical properties of the RCuGe intermetallics. The accounting for electron–electron correlations in Tb, Dy, Ho, Er resulted in a good agreement between the calculated and experimental magnetic and optical characteristics.

Optical Properties of YFe2 and TbFe2 Compounds

The ellipsometric studies of the optical properties of intermetallic YFe2 and TbFe2 compounds have been performed in the wavelength range 0.22–15 μm, and a number of electronic and spectral characteristics have been determined. The nature of the interband light absorption in these materials is discussed based on a comparative analysis of the experimental and theoretical spectra of the optical conductivity. The experimental optical conductivities of the compounds in the region of quantum electron transitions are shown to agree qualitatively with the spectra calculated from the densities of electronic states.

Electronic Structure of the DyFe2Si2 Compound: Energy Band Calculations and Optical Studies

The electronic structure and the optical properties of the DyFe2Si2 compound have been studied. The calculations of the energy band spectrum taking into account the spin polarization have been performed in an approximation of the local electron density with a correction for strong correlation effects in the 4f shell of a rare-earth metal (the GGA + U method). The optical properties have been studied by the ellipsometric method in a wide range of wavelengths; a number of spectral and electronic characteristics have been determined. It is shown that the optical conductivity of this compound in the region of the interband light absorption is adequately explained in the framework of the performed calculation of electronic states.

Оптические свойства соединений YFe-=SUB=-2-=/SUB=- и TbFe-=SUB=-2-=/SUB=-

Ellipsometric investigation of the optical properties of YFe2 and TbFe2 intermetalic compounds have been carried out in wavelength range of 0.22 –15 μm. A number of electronic and spectral characteristic was determined. Nature of interband light absorption in these materials is discussed on base of comparative analyses of experimental and theoretical optical conductivity spectra. Experimental optical conductivities of the compounds are shown to conform qualitatively to spectra calculated from densities of electronic states in the region of quantum electron transitions.

An Ellipsometric Investigation of the Optical Properties of Ru2Ge3 and Ru2Sn3 Compounds

Ellipsometric investigations of the optical properties of Ru2Ge3 and Ru2Sn3 intermetallic compounds are carried out in the wavelength range from 0.22 to 15 μm. The nature of interband light absorption is analyzed based on a comparative analysis of the experimental and theoretical frequency dependences of an optical conductivity. The obtained results confirm the existence of energy gaps at the Fermi level in the electronic spectra of these materials predicted earlier by the band-structure calculations.

The Structure of Electronic States and Optical Properties of Cr80Al20 Compound

Ellipsometric studies of the optical properties of the intermetallic Cr80Al20 compound in the spectral range of 0.22–15 μm have been performed. The self-consistent calculation of the electronic structure and density of the electronic states of the material has been carried out. The spectrum of interband light absorption is interpreted on the basis of comparative analysis of theoretical and experimental dispersion dependences of optical conductivity. A number of characteristics of conduction electrons have been determined.

Features of the Current Flow in Injection Structures Based on PbSnTe:In Films

This paper reports a study of the current–voltage (I–V) features of the p-i-p structures based on Pb1–xSnxTe:In films with the tin content х ≈ 0.31 in which the metal–insulator transition occurs. It is shown that the photocurrent is the hole current under light interband excitation, and electron trapping is dominant. The experimental and theoretical data are compared.

Topological and non inertial effects on the interband light absorption

In this work, we investigate the combined influence of the nontrivial topology introduced by a disclination and non inertial effects due to rotation, in the energy levels and the wave functions of a noninteracting electron gas confined to a two-dimensional pseudoharmonic quantum dot, under the influence of an external uniform magnetic field. The exact solutions for energy eigenvalues and wave functions are computed as functions of the applied magnetic field strength, the disclination topological charge, magnetic quantum number and the rotation speed of the sample. We investigate the modifications on the light interband absorption coefficient and absorption threshold frequency. We observe novel features in the system, including a range of magnetic field without corresponding absorption phenomena, which is due to a tripartite term of the Hamiltonian, involving magnetic field, the topological charge of the defect and the rotation frequency.

Screw dislocation and external fields effects on the Kratzer pseudodot

In this research, we investigate the influence of the screw dislocation on the energy levels of nonrelativistic electrons on a two-dimensional solid taking into account the deformed Kratzer potential under an external magnetic and the Aharonov–Bohm (AB) fields. We obtain the bound state energy eigenvalues equation and the corresponding wave functions by using the Frobenius method. We also calculate the direct interband light absorption coefficient and threshold frequency of absorption in a quantum pseudodot. Some of the numerical results are given.