Interband Absorption Coefficient Research Articles

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.

Impurity photoionization cross-section and intersubband optical absorption coefficient in multilayer spherical quantum dots

Energy spectrum, wave functions and binding energies of the electron to the donor impurity ion located in the center of a multilayer spherical quantum dot (MSQD) consisting of a core and two spherical shells were studied within the effective mass approximation. Based on the exact wave functions of the electron expressed in terms of Coulomb functions of the first and second kind, the spectral dependences of the photoionization cross section of the impurity (PCS) and the intersubband optical absorption coefficient (OAC) for various geometric dimensions of the nanostructure were calculated. It is shown that the decrease in the width of the external potential well changes the localization of the electron in the nanosystem which significantly affects the binding energy of the electron with the impurity, photoionization cross section and interband absorption coefficient. The position of the PCS peak associated with the quantum transition of an electron from the ground state to the 1p0 state shifts to the region of higher energies, and its height decreases. At the same time, the height of PCS peaks associated with quantum transitions to higher excited states (2p0, 3p0) increases.The presence of impurities and changes in the MSQD size significantly affect the intersubband absorption coefficient. Decrease of the external potential well width in the absence of impurities leads to a monotonous increase in OAC through the first excited state, and in the presence of a central impurity, absorption through states with higher energy increases.

Theoretical investigation of interband absorption coefficient and physical properties of GaAsNBi alloy with lattice-matched to GaAs

The physical and optical properties of GaAsNBi alloy have been calculated theoretically using the 16-band k.p model. Hence, summing due to the intake of all transitions from the upper subbands of VB to degenerate CB using selection rule leads to nonmonotonic dependence with photon energy with an average value of 38×104cm-1. The corresponding physical properties, such as the intrinsic carrier concentration variation seen monotonic with 2%Bi and 1.2%N compositions and at room temperature nearly 4.23×1010cm-3. Reduction of the Debye temperature (TD) of GaAsNBi alloy as a function of N and Bi composition along crystallographic direction define the stability of crystalline GaAsNBi alloy. Also, the Bulk modulus can be modulated from 780 to 660 GPa as a function of Bi compositions for different N mole fraction.

Electronic band structure and optical properties of GaAsSb/GaAs for optoelectronic device applications: A 14 band k.p study

The band structure of GaAsSb/GaAs material is calculated along a crystallographic direction using a 14-band model approach. This model captures the reduction of bandgap by 13.5 meV/%Sb and provides a tool for device-level design under a range of wavelength ~ 0.9 μ m to 1.3 μ m for antimony composition limit 0.1%<Sb<35%, respectively. The analysis extends to calculating the outcome of the antimony composition on electron and hole effective mass. We have found that the electron effective mass (0.057 m o , 35% Sb) decreases by ~ 1.2 compared to GaAs (0.067 m o ). Which is responsible for improving the optical gain. So, from the obtained effective mass we determined intrinsic carrier concentration, which seems monotonic with antimony composition. Furthermore, due to uncertainty in VB and CB offset values a lateral variation of 160 nm between type I and type II QWs was observed in the optical gain spectrum. While for use in solar cells, the interband absorption coefficient was also examined as a function of photon energy with a fundamental absorption edge observed at 0.96 eV. The results obtained are well consistent with the literature result previously reported. • GaAs 1 − x Sb x band structures have been calculated by 14 band k.p hamiltonian. • Observed bandgap reduction of GaAs 1-x Sb x by 13.5 meV/%Sb. • Incorporation of Sb (35%) into the host GaAs leads to a decrease in electron effective mass by ~ 1.2 times. • Intrinsic carrier concentration analysis revealed that GaAsSb material pushes towards the p-type base. • Lateral variation by 160nm in optical gain spectrum between type-I and type-II QWs is observed.

Theoretical Investigation of BGaAs/GaAs for Optoelectronic Device Applications

Boron dopant incorporation into host GaAs material to form a novel BGaAs semiconductor has been studied using a 10-band kp model. This model allows us to calculate the electronic band structure along the crystallographic direction. So, from the obtained E–k relation, we calculate the carrier effective mass, intrinsic carrier concentration, and x = 0 (GaAs) are in good agreement with previously reported literature. The intrinsic carrier concentration variation is seen as monotonic with boron composition. On the other hand, the composition-dependent Debye temperature observed reduction along with symmetry directions, Λ by 1.23/%B, Σ by − 2.33/%B, and Δ by − 3.52/%B, which leads to the lower stability of crystalline BGaAs alloy. In addition, the interband absorption coefficient as a function of photon energy shows nonmonotonic dependence with fundamental absorption observed at 1.39 eV. Whereas, in the case of quantum well, the optical gain spectrum peak is blueshifted with the density of injected carriers. Hence, this study provides beneficial guidance in the interpretation of applications such as solar cells, optical modulators, multiple QWs.

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.

Micron-sized liquid nitrogen-cooled indium antimonide photovoltaic cell for near-field thermophotovoltaics.

Simulations of near-field thermophotovoltaic devices predict promising performance, but experimental observations remain challenging. Having the lowest bandgap among III-V semiconductors, indium antimonide (InSb) is an attractive choice for the photovoltaic cell, provided it is cooled to a low temperature, typically around 77 K. Here, by taking into account fabrication and operating constraints, radiation transfer and low-injection charge transport simulations are made to find the optimum architecture for the photovoltaic cell. Appropriate optical and electrical properties of indium antimonide are used. In particular, impact of the Moss-Burstein effects on the interband absorption coefficient of n-type degenerate layers, and of parasitic sub-bandgap absorption by the free carriers and phonons are accounted for. Micron-sized cells are required to minimize the huge issue of the lateral series resistance losses. The proposed methodology is presumably relevant for making realistic designs of near-field thermophotovoltaic devices based on low-bandgap III-V semiconductors.

Modelling of heating and photoexcitation of single-crystal silicon under multipulse irradiation by a nanosecond laser at 1.06 μm

We report a theoretical study of heating and photoexcitation of single-crystal silicon by nanosecond laser radiation at a wavelength of 1.06 μm. The proposed physicomathematical model of heating takes into account the complex nonlinear dynamics of the interband absorption coefficient of silicon and the contribution of the radial heat removal to the cooling of silicon between pulses under multipulse irradiation, which allows one to obtain a satisfactory agreement between theoretical predictions of silicon melting thresholds at different nanosecond pulse durations and experimental data (both under single-pulse and multipulse irradiation). It is found that under irradiation by nanosecond pulses at a wavelength of 1.06 μm, the dynamic Burshtein – Moss effect can play an important role in processes of photoexcitation and heating. It is shown that with the regimes typical for laser multipulse microprocessing of silicon (the laser spot diameter is less than 100 μm, and the repetition rate of pulses is about 100 kHz), the radial heat removal cannot be neglected in the analysis of heat accumulation processes.

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.

Exceptional Optical Response of Archimedean Boron and Group-V Ultrathin Nanosheets

The ascendancy of ultrathin films has emerged as a boon for 21st century nanotechnologies that rely on flexibility, tunable properties, and active surface area. We explore uncharted configurations with Archimedean (4,8)-tessellations that exhibit exceptional light–matter interactions captured with time-dependent density functional theory. We find that planar monolayers of haeckelite boron-pnictogen binary materials possess strong interband absorbance and absorption coefficients that rival existing ultrathin films. These observables were found to occur in the ultraviolet for the boron-nitride nanosheet and in the infrared region of the electromagnetic spectrum for heavier pnictogens, suggesting a route for photocapture of high density solar photons. Moreover, we find the buckled haeckelite boron arsenide supports a similar, yet slightly decreased, optical response that is blue-shifted from its planar configuration. The strong optical response of these ultrathin films emerges from their unique bandstructure...

Coefficient of Interband Light Absorption by InAs/GaхIn1-хAs Quantum Dot Superlattice at Low Temperatures

In the paper the InAs/GaxIn1-xAs superlattice system of small size cubic QDs (10 nm) has been considered. Dispersion relations for electron and hole subbands have been calculated for superlattices of different dimensionality. The dependences of the interband absorption coefficient on light frequency, quantum dot size and interdot distance have been researched.It is shown, that the dimension of the superlattice has influence on the shape of the absorption bands and the increasingof the distance between quantum dots is followed by narrowing of the absorption peaks for all three superlatticetypes.

Landau quantization, Aharonov–Bohm effect and two-dimensional pseudoharmonic quantum dot around a screw dislocation

We investigate the influence of a screw dislocation on the energy levels and the wavefunctions of an electron confined in a two-dimensional pseudoharmonic quantum dot under the influence of an external magnetic field inside a dot and Aharonov–Bohm field inside a pseudodot. The exact solutions for energy eigenvalues and wavefunctions are computed as functions of applied uniform magnetic field strength, Aharonov–Bohm flux, magnetic quantum number and the parameter characterizing the screw dislocation, the Burgers vector. We investigate the modifications due to the screw dislocation on the light interband absorption coefficient and absorption threshold frequency. Two scenarios are possible, depending on if singular effects either manifest or not. We found that as the Burgers vector increases, the curves of frequency are pushed up towards of the growth of it. One interesting aspect which we have observed is that the Aharonov–Bohm flux can be tuned in order to cancel the screw effect of the model.

Effects of crossed electric and magnetic fields on the interband optical absorption spectra of variably spaced semiconductor superlattices

The interband optical absorption spectra of a GaAs–Ga1−xAlxAs variably spaced semiconductor superlattice under crossed in-plane magnetic and growth-direction applied electric fields are theoretically investigated. The electronic structure, transition strengths and interband absorption coefficients are analyzed within the weak and strong magnetic-field regimes. A dramatic quenching of the absorption coefficient is observed, in the weak magnetic-field regime, as the applied electric field is increased, in good agreement with previous experimental measurements performed in a similar system under growth-direction applied electric fields. A decrease of the resonant tunneling in the superlattice is also theoretically obtained in the strong magnetic-field regime. Moreover, in this case, we found an interband absorption coefficient weakly dependent on the applied electric field. Present theoretical results suggest that an in-plane magnetic field may be used to tune the optical properties of variably spaced semiconductor superlattices, with possible future applications in solar cells and magneto-optical devices.

Effect of Interdiffusion on Optoelectronic Properties of In1-xGaxAs/InAs/In1-yAlyAs Quantum Well

The effect of interdiffusion of Al, Ga and In atoms on confining potential, ground state energy level of electron and interband light absorption coefficient in In1-xGaxAs/InAs/In1-yAlyAs quantum well is investigated in the framework of variational method and Wood-Saxon potential model. It is shown that the interdiffusion leads to the smearing of potential rectangular profile, to the rising up of ground state energy level and to the significant decrease in the interband absorption coefficient.

Two-photon interband absorption coefficients in tungstate and molybdate crystals

Two-photon absorption (TPA) coefficients were measured in tungstate and molybdate crystals – BaWO4, KGW, CaMoO4, BaMoO4, CaWO4, PbWO4 and ZnWO4 upon different orientations of excitation polarization with respect to the crystallographic axes. Trains of 25ps pulses with variable radiation intensities of third (349nm) harmonics of passively mode-locked 1047nm Nd:YLF laser were used for interband two-photon excitation of the crystals.It was suggested that in the case, when 349nm radiation pumping energy exceeds the bandgap width (hν>Eg), the nonlinear excitation process can be considered as two-step absorption.The interband two-photon absorption in all the studied crystals induces the following one-photon absorption from the exited states, which affects the nonlinear process dynamics and leads to a hysteresis in the dependence of the transmission on the excitation intensity. This fact was taken into account under analysis of the experimental dependences of the reciprocal transmission on the excitation intensity. Laser excitation in the transparency region of the crystals caused stimulated Raman scattering (SRS) not for all the crystals studied. The measured nonlinear coefficients allowed us to explain the suppression of SRS in crystals as a result of competition between the SRS and TPA.

Empiric k·p Hamiltonian calculation of the band-to-band photon absorption in semiconductors

The Empiric k·p Hamiltonian method is usually applied to nanostructured semiconductors. In this paper, it is applied to a homogeneous semiconductor in order to check the adequacy of the method. In this case, the solutions of the diagonalized Hamiltonian, as well as the envelope functions, are plane waves. The procedure is applied to the GaAs and the interband absorption coefficients are calculated. They result in reasonable agreement with the measured values, further supporting the adequacy of the Empiric k·p Hamiltonian method.

Specific features of the electronic states and interband absorption coefficient in a cylindrical nanotube of finite thickness with a vertical potential of confinement

In this paper the features of one-electron states in a circular cylindrical sector are investigated. The finite thickness of the cylinder and the spatial expansion of the barrier, which runs along the cylinder generatrix, are taken into account. In the framework of the proposed model the distribution of electrons in the quantum states, as well as features of interband absorption of electromagnetic radiation, is theoretically investigated.

Inter-band optoelectronic properties in quantum dot structure of low band gap III-V semiconductors

A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k→) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg1−xCdxTe, and In1−xGaxAsyP1−y lattice matched to InP, as example of III–V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.

Effects of the magnetic field direction and anisotropy on the interband light absorption of an asymmetric quantum dot

In this paper, the direct interband transition and the threshold frequency of absorption in a two-dimensional anisotropic quantum dot are studied under the influence of a tilted external magnetic field. We first calculate the analytical wave functions and energy levels using a transformation to simplify the Hamiltonian of the system. Then, we obtain the analytical expressions for the light interband absorption coefficient and the threshold frequency of absorption as a function of the magnetic field, magnetic field direction, and anisotropy of the system. According to the results obtained from the present work, we find that (i) the absorption threshold frequency (ATF) increases when the magnetic field increases for all directions. (ii) When anisotropy is increased, ATF increases. (iii) At small anisotropy, the magnetic field direction has no important effect on the ATF. In brief, the magnetic field, magnetic field direction, and anisotropy play important roles in the ATF and absorption coefficient.

A quantum pseudodot system with two-dimensional pseudoharmonic oscillator in external magnetic and Aharonov-Bohm fields

Using the Nikiforov-Uvarov (NU) method, the energy levels and the wave functions of an electron confined in a two-dimensional (2D) pseudoharmonic quantum dot are calculated under the influence of temperature and an external magnetic field inside dot and Aharonov-Bohm (AB) field inside a pseudodot. magnetic field and geometrical size of quantum pseudodot. The temperature dependence energy levels for GaAs semiconductor are also calculated. The exact solutions for energy eigenvalues and wave functions are computed as functions of the chemical potential parameters, applied magnetic field strength, AB flux field, magnetic quantum number and temperature. Analytical expression for the light interband absorption coefficient and absorption threshold frequency are found as functions of applied