Intraband Absorption Coefficient Research Articles

Light absorption by free charge carriers in the presence of phonons in an anisotropic quantum wire

The absorption of light by free charge carriers has been theoretically studied considering the processes related to scattering from phonons in an anisotropic parabolic quantum wire. The case in which the electromagnetic wave is polarized along the axis of the wire and the case of non-degenerate electron gas statistics have been considered. In this work, it was determined that the dependence of the location of the peaks of the intraband optical absorption coefficient on the characteristic frequency of the confinement potential in quantum wires with asymmetric parabolic potential was .

Tuning electrical and optical properties of InAs/GaAs1−x Sb x quantum dots

Understanding the electrical and optical properties of InAs/GaAs(Sb) quantum dots (QDs) is essential for designing and improving the performance of related semiconductor QD devices. In this paper, the effects of In segregation, QD size, capping layer thickness and Sb composition on the electrical and optical properties of type I and type II InAs/GaAs1−x Sb x () QDs are systematically investigated and general regularities are summarized. The comparisons of electron distribution probabilities, interband and intraband transition energies and absorption coefficients show that In segregation and QD size have a strong influence on the electron energy level positions of InAs QDs and that the trade-offs between absorption peak energy, absorption intensity and radiative lifetime of InAs/GaAs1−x Sb x QDs can be optimized by adjusting the thickness and Sb composition of the GaAs1−x Sb x capping layer. The results obtained are promising for the applications in the pre-design and performance feedback of the QD devices such as QD lasers, QD infrared detectors and intermediate band solar cells.

Strain effect on the intraband absorption coefficient for spherical CdSe/CdS/ZnSe core–shell–shell quantum dots

In this work, we theoretically calculated the intraband absorption coefficient (IAC) between the 1s and 1p conduction band states for a spherical core/shell/shell quantum dot (CSS-QD) as function of inner and outer shells’ sizes with and without the presence of strain effect. The electronic structure for the system is computed in the effective mass approximation framework and the strain effect is considered on the continuum elasticity model. We found out that as we compared the strained and the unstrained system, the former causes that the IAC undergoes a small redshift. A similar behavior occurs as the inner and outer shell size increase. The results show that the strain effect is an important factor that will be considered in these nanostructure type. The incorporation of inner and outer shells allowed us to extend some fractions of eV into the absorption spectrum that could be interesting as a mechanism to control the IAC device design.

Theory of nonlinear microwave absorption in an electron-doped and gapped graphene monolayer

Abstract We present a theory of nonlinear microwave absorption in monolayer graphene grown epitaxially on a SiC substrate and electron-doped by electrostatic gating. The intensity-dependent absorption coefficient of normally incident microwave radiation is calculated by using the Boltzmann equation techniques. The Boltzmann transport equation for mobile carriers in the conduction band of the graphene layer is solved to third order in the applied microwave field, including nonlinearities due to both the nonparabolicity of the conduction band and the energy-dependent scattering rate of electrons by acoustic phonons and short-range lattice defects. The intraband absorption coefficient decreases with an increase in the intensity of incident radiation, thus suggesting that electron-doped epitaxial graphene may be exploited as a saturable absorber operating at microwave frequencies. The saturation intensity is calculated as a function of excitation frequency and electron concentration and found to be a few MW/cm 2 over the millimeter wave frequency band considered (30–300 GHz) at a typical doping level of 1012 cm−2.

Size- and Temperature-Dependent Intraband Optical Properties of Heavily n-Doped PbS Colloidal Quantum Dot Solid-State Films.

Steady-state access to intraband transitions in colloidal quantum dots (CQDs), via doping, permits exploitation of the electromagnetic spectrum at energies below the band gap. CQD intraband optoelectronics allows envisaging cheap mid- and long-wavelength infrared photodetectors and light-emitting devices, which today employ epitaxial materials. As intraband devices start to emerge, thorough studies of the basic properties of intraband transitions in different CQD materials are needed to guide technological research. In this work, we investigate the size and temperature dependence of the intraband transition in heavily n-doped PbS quantum dot (QD) films. In the studied QD size range (5-8 nm), the intraband energy spans from 209 to 151 meV. We measure the intraband absorption coefficient of heavily doped PbS QD films to be around 2 × 104 cm-1, proving that intraband absorption is as strong as interband absorption. We demonstrate a negative dependence of the intraband energy with temperature, in contrast to the positive dependence of the interband transition. Also opposite to the interband case, the temperature dependence of the intraband energy increases with decreasing size, going from -29 μeV/K to -49 μeV/K in the studied size range.

Effect of the hydrostatic pressure and shell’s Al composition in the intraband absorption coefficient for core/shell spherical GaAs/Al[formula omitted]Ga[formula omitted]As quantum dots

In this paper we theoretically investigate the role of hydrostatic pressure by analyzing its influence on potential barrier’s height in GaAs/AlxGa1−xAs core/shell spherical quantum dots. The values of hydrostatic pressure considered here are always below the Γ−X crossover. In addition, we take into account the barrier shell’s size effects and the barrier’s aluminum concentration, looking for a description of the features of the intraband optical absorption coefficient in the system. The electronic structure is calculated within the effective mass approximation. From the numerical point of view the hybrid matrix method was implemented to avoid numerical instability issues that appears in the conventional transfer matrix method. The main intersubband optical transition is considered to take place between the 1s and 1p computed electronic states. The results show that the absorption coefficient undergoes first a red-shift and later a more pronounced blue-shift, depending on the AlxGa1−xAs barrier width (wb1). The absorption coefficient experiences a blue-shift as the barrier’s aluminum concentration increases, and it is non monotonically red-shifted as the hydrostatic pressure augments, due to the barrier’s height pressure dependency. For the chosen system parameters, the absorption coefficient resonant peak lies within the range of 20 to 30 meV, that corresponds to the THz frequency region. Accordingly, this system can be proposed as a building block for photodetectors in the THz electromagnetic spectrum region.

Interband and Intraband Absorption Coefficients of Silicon: Theoretical Frameworks and Formulations

Theoretical frameworks and formulations for calculating Si interband and intraband absorption coefficients arepresented and discussed in this work. They are based on the second-order time-dependent perturbation theory of quantum mechanics which incorporates interaction matrices between electrons, photons, phonons, and charged impurities. These frameworks include the interband and intraband processes of direct and indirect transitions. The intraband indirect-transition processes include phonon-assisted and charged-impurity-assisted intravalley processes, inter-non-equivalent-valley processes, inter-opposite-equivalent-valley g-processes, and inter-non-opposite-equivalent-valley f-processes. These theoretical formulations are verified with the interband absorption coefficients from Green's data and the Rajkanan-Singh-Shewchun formula. They are also verified with the intraband free-carrier absorption coefficients from the Spitzer-Fan data in n -type Si at different doping concentrations, Green's formula, the Schroder-Thomas-Swartz formula, the Soref-Bennett formula for 1.3 and 1.55 μm wavelengths, and Ridley's equations. The agreements and discrepancies between this theoretical work and other experimental data, empirical formulas, theoretical equations are examined and investigated. This work will provide a fundamental theoretical framework and formulation for calculating Si interband and intraband absorption coefficients which could be useful for the design and modeling of Si photonic devices.

Intraband Radiation Absorption by Holes in InAsSb/AlSb and InGaAsP/InP Quantum Wells

Microscopic analysis of intraband radiation absorption by holes with their transition to the spin-split band for InAsSb/AlSb and InGaAsP/InP semiconductor quantum wells is performed in the context of the four-band Kane model. The calculation is performed for two incident-radiation polarizations: along the crystal-growth axis and in the quantum-well plane. It is demonstrated that absorption with transition to the discrete spectrum of spin-split holes has a higher intensity than absorption with transitions to the continuous spectrum. The dependences of the intraband absorption coefficient on temperature, hole density, and quantum- well width are thoroughly analyzed. It is shown that intraband radiation absorption can be the main mechanism of internal radiation losses in lasers based on quantum wells.

Внутризонное поглощение излучения дырками в квантовых ямах InAsSb/AlSb и InGaAsP/InP

AbstractMicroscopic analysis of intraband radiation absorption by holes with their transition to the spin-split band for InAsSb/AlSb and InGaAsP/InP semiconductor quantum wells is performed in the context of the four-band Kane model. The calculation is performed for two incident-radiation polarizations: along the crystal-growth axis and in the quantum-well plane. It is demonstrated that absorption with transition to the discrete spectrum of spin-split holes has a higher intensity than absorption with transitions to the continuous spectrum. The dependences of the intraband absorption coefficient on temperature, hole density, and quantum- well width are thoroughly analyzed. It is shown that intraband radiation absorption can be the main mechanism of internal radiation losses in lasers based on quantum wells.

Absorption of light by free electrons in semiconductors I Processes involving longitudinal optical phonons

We calculated the absorption coefficient of light in intraband transitions involving longitudinal optical phonons in semiconductors for various arbitrary free electron densities. We describe the intraband absorption coefficients as a function of frequency and temperature for a crystal with the band structure and vibration mode parameters typical of A2B6 crystals.

Laser driven intraband optical transitions in two-dimensional quantum dots and quantum rings

The intraband optical absorption have been investigated in the presence of hydrogenic donor impurity in GaAs/GaAlAs quantum dot and quantum ring in the intense laser field. The single electron energy spectrum and wave functions have been found using the effective mass approximation and exact diagonalization technique. Different selection rules are obtained for intraband transitions depending on the direction of incident light polarization. Due to the accidental degeneracy of the laser dressed impurity states the crossings of the curves of the threshold energies and the dipole matrix elements on laser field parameter have been observed. The intraband absorption coefficient is calculated for different locations of hydrogenic donor impurity and different values of intense laser field parameter. The obtained results show that the absorption spectrum can exhibit either a blue- or redshift depending on the impurity location, values of the laser field parameter and direction of incident light polarization. The obtained theoretical results indicate a novel opportunity to tune the performance of new devices, based on the quantum dots and quantum rings and to control their specific properties by means of intense laser and hydrogenic donor impurity.

Donor impurity-related intraband optical absorption in a single quantum ring: Hydrostatic pressure and intense laser field effects

The simultaneous influence of hydrostatic pressure and intense laser field on hydrogenic donor impurity states and intraband optical absorption has been investigated in GaAs/\(\mathrm{Ga}_{1-\tilde{x}}\mathrm{Al}_{\tilde{x}}\)As quantum ring. The one-electron energy spectrum and wave functions have been found using the effective mass approximation and exact diagonalization technique. The intraband absorption coefficient is calculated for different values of the hydrostatic pressure, intense laser field parameter and different locations of hydrogenic donor impurity. The simultaneous influence of hydrostatic pressure and intense laser field shows that while the increment of the first one leads only to the blueshift of the absorption spectrum, the augmentation of the second one makes the redshift. In addition, both blueshift and redshift of the spectrum have been obtained with the changes of impurity location. The obtained theoretical results indicate good controlling means of the optical spectrum of ring-like structures by the combined influence of the considered factors.

Intraband optical absorption in a single quantum ring: Hydrostatic pressure and intense laser field effects

The intraband optical absorption in GaAs/Ga0.7Al0.3As two-dimensional single quantum ring is investigated. Considering the combined effects of hydrostatic pressure and intense laser field the energy of the ground and few excited states has been found using the effective mass approximation and exact diagonalization technique. The energies of these states and the corresponding threshold energy of the intraband optical transitions are examined as a function of hydrostatic pressure for the different values of the laser field parameter. We also investigated the dependencies of the intraband optical absorption coefficient as a function of incident photon energy for different values of hydrostatic pressure and laser field parameter. It is found that the effects of hydrostatic pressure and intense laser field lead to redshift and blueshift of the intraband optical spectrum respectively.

Intraband Absorption Coefficient in Organic–Inorganic Hybrid Nanocomposite—A Pathway to Room-Temperature, Mid- and Long-Wavelength Infrared Detection

Size reduction in materials into nanometer range leads to discrete energy levels depending on the size of the structure. Control over dimensions as well as the composition of structures makes it possible to tailor material properties for specific applications. Colloidal quantum dots (CQDs) are solution phase processed nanostructure, which are coated with a surface ligand material that is comprised of short, organic molecules to prevent the CQDs from aggregation when placed in solution. In fact, mostly, they are embedded in a matrix material, which necessarily affects the electronic levels of the nanostructure. Hybrid nanocomposite is mainly composed of inorganic CQDs embedded in an organic conjugated polymer. In this paper, we present a method for calculating the electronic structure, such as intraband energy levels and wave functions in a hybrid nanocomposite thin-film structure. This model converts the Schrodinger equation into a matrix equation, which can be easily solved by programming languages. Moreover, based on the model, optical intraband absorption coefficient for an embedded CQD into conducting polymer is calculated and compared with experimental data. Our analysis shows that hybrid nanocomposite can be considered as a good candidate for absorber material in mid- and long-wavelength infrared detectors. In addition, the impact of the CQD average size is also studied as design parameter on the absorption spectra of the hybrid nanocomposites. The model is verified by comparing the results with reported data in the literature.

Influence of lateral electric field on intraband optical absorption in concentric double quantum rings

The influence of lateral electric field on one-electron states and intraband absorption in two-dimensional concentric double quantum rings is investigated. The confining potential of the rings is modeled as a double harmonic central potential. Using the exact diagonalization technique, we calculate the dependence of the electron energy spectrum as a function of the electric field strength as well as the inner ring radius. Also, different values of confinement strength are considered. Selection rule is obtained for intraband transitions, caused by the direction of incident light polarization. The intraband absorption coefficient is calculated for different values of electric field strength, inner ring radius, confinement strength and incident light polarization direction. The combined influence of electric field strength and change of confining strength show that while the increment of the first one leads only to blueshift of absorption spectrum, the augment of the second one makes the redshift. In addition, both blueshift and redshift of the spectrum have been obtained with the enlargement of inner ring radius. Finally, we show that the absorption spectrum undergoes redshift by changing the polarization of incident light from x- to y-axis.

The effects of the intense laser and homogeneous electric fields on the electronic and intraband optical properties of a GaAs/Ga0.7 Al0.3As quantum ring

The simultaneous influences of an intense laser field and static electric field on one-electron states and intraband optical absorption coefficient are investigated in two-dimensional GaAs/GaAl0.3 As quantum ring. An analytical expression of the effective confining potential in the presence of the external fields is obtained. The one-electron energy levels and wave functions are calculated using the effective mass approximation and an exact diagonalization technique. We show that changes in the incident light polarization lead to blue- or redshifts in the intraband optical absorption spectrum. Moreover, we found that blueshift and redshift are induced by the simultaneous influences of an intense laser and lateral electric fields. The obtained theoretical results indicate a novel opportunity to tune the performance of quantum rings and to control their specific properties by means of intense laser and homogeneous electric fields.

Electronic and intraband optical properties of single quantum rings under intense laser field radiation

The influence of an intense laser field on one-electron states and intraband optical absorption coefficients is investigated in two-dimensional GaAs/Ga0.7Al0.3As quantum rings. An analytical expression of the effective lateral confining potential induced by the laser field is obtained. The one-electron energy spectrum and wave functions are found using the effective mass approximation and exact diagonalization technique. We have shown that changes in the incident light polarization lead to blue- or redshifts in the intraband optical absorption spectrum. Moreover, we found that only blueshift is obtained with increasing outer radius of the quantum ring.

Intraband absorption in GaAs-(Ga,Al)As variably spaced semiconductor superlattices under crossed electric and magnetic fields

A theoretical study of the intraband absorption properties of GaAs-Ga1−xAlxAs variably spaced semiconductor superlattices under crossed magnetic and electric fields is presented. Calculations are performed for the applied electric field along the growth-axis direction, whereas the magnetic field is considered parallel to the heterostructure layers. By defining a critical electric field so that the heterostructure energy levels are aligned in the absence of the applied magnetic fields, one finds that, in the weak magnetic-field regime, an abrupt red shift of the absorption coefficient maxima is obtained at fields equal to or larger than the critical electric field, a fact which may be explained from the localization properties of the electron wave functions. Results in the strong magnetic-field regime reveal a rich structure on the intraband absorption coefficient which may be explained from the strong dispersion exhibited by both the energy levels and transition strengths as functions of the generalized orbit-center position. Moreover, the possibility of occurrence of absorption in a wide frequency range is also demonstrated. Present calculated results may be of interest for future design and improvement of multilayered-based photovoltaic and solar-cell devices.

Donor impurity-related linear and nonlinear intraband optical absorption coefficients in quantum ring: effects of applied electric field and hydrostatic pressure.

The linear and nonlinear intraband optical absorption coefficients in GaAs three-dimensional single quantum rings are investigated. Taking into account the combined effects of hydrostatic pressure and electric field, applied along the growth direction of the heterostructure, the energies of the ground and first excited states of a donor impurity have been found using the effective mass approximation and a variational method. The energies of these states are examined as functions of the dimensions of the structure, electric field, and hydrostatic pressure. We have also investigated the dependencies of the linear, nonlinear, and total optical absorption coefficients as a function of incident photon energy for several configurations of the system. It is found that the variation of distinct sizes of the structure leads to either a redshift and/or a blueshift of the resonant peaks of the intraband optical spectrum. In addition, we have found that the application of an electric field leads to a redshift, whereas the influence of hydrostatic pressure leads to a blueshift (in the case of on-ring-center donor impurity position) of the resonant peaks of the intraband optical spectrum.

Simultaneous effects of hydrostatic pressure and spin–orbit coupling on linear and nonlinear intraband optical absorption coefficients in a GaAs quantum ring

In this paper the simultaneous effect of hydrostatic pressure and Rashba spin–orbit interaction on intraband linear and nonlinear light absorption has been investigated in cylindrical quantum ring. The one electron energy spectrum has been found using the effective mass approximation and diagonalization procedure. We have found that the Rashba interaction can lead both to the blue- or to the red-shift of the absorption spectrum depending on the transitions character, while the only red-shift is observed due to the hydrostatic pressure.