Inverse Parabolic Quantum Wells Research Articles

Influence of external fields on the exciton binding energy and interband absorption in a double inverse parabolic quantum well

Ground-state binding energy and optical absorption coefficient of exciton in a symmetric double inverse parabolic quantum well system in the presence of external electric and magnetic fields are investigated theoretically. Numerical calculations have been carried out with the variational technique considering the single-band effective mass approximations. Results reveal that the excitonic binding energy and interband optical absorption depend on significantly on the geometrical and structural parameters defining carriers’ double inverse parabolic confinement potential, the aluminum concentration at the well center, the electric field, and the magnetic field. The exciton binding energy is a decreasing (increasing) function of the electric field (magnetic field). The increase in aluminum concentration creates a blueshift at the resonance peak positions. As a result, the tunability of the excitonic effects is expected to be of importance in developing stable and high-efficiency nanoscale excitonic optoelectronic devices . • Analyses of double inverse parabolic quantum well. • Exciton binding energy. • Interband transitions. • Electric and magnetic field effects.

Intense laser field effect on the nonlinear optical properties of triple quantum wells consisting of parabolic and inverse-parabolic quantum wells

The nonlinear optical rectification, the second harmonic generation coefficient, and the third harmonic generation coefficient in parabolic-inverse parabolic-parabolic quantum wells (PIPPQWs) and inverse parabolic-parabolic-inverse parabolic quantum wells (IPPIPQWs) are calculated varying the intense laser field (ILF) parameter (). The modifications of the dipole moment matrix elements and the energy levels are depending on the potential shape. The results show that the ILF intensity exerts an active influence on the profile, height, and width of the confinement potential of both PIPPQW and IPPIPQW. The potential profile of IPPIPQW has been affected otherwise than PIPPQW for different ILF intensities. The nonlinear optical rectification, the second harmonic generation, and the third harmonic generation coefficients of PIPPQW and IPPIPQW could be altered in the energy range and the size of the resonance peak by rising the ILF intensity. By changing the parameter, it is conceivable to organize red or blue shift at the resonance peak positions of the nonlinear optical rectification, the second harmonic generation, and the third harmonic generation coefficients. The shift of the nonlinear optical rectification coefficient occurs when the difference between the ground and the second energy levels changes. According to the parameters used here, while for PIPPQW the spectrum of the resonance peak of the nonlinear optical rectification displays a blue shift with increasing ILF, this spectrum displays a red shift for IPPIPQW. The consequences can be valued in investigating new ways of changing the optical and electronic properties of semiconductor quantum wells.

Optical absorption coefficients in GaN/Al(Ga)N double inverse parabolic quantum wells under static external electric field

In this work, we have investigated theoretically the effects of applied electric field on the linear and nonlinear optical properties in a GaN/Al[Formula: see text]Ga[Formula: see text]N double inverse parabolic quantum well for different Al concentrations at the well center. Our calculations are based on the potential morphing method in the effective mass approximation. The systematic theoretical investigation contains results with all possible combinations of the involved parameters, such as quantum well width, quantum barrier width, Al concentration at each well center and magnitude of the external electric field. Our results show that the electric fields strengths, the parameter of nanostructure and incident optical intensity have a great effect on the optical characteristics of these nanostructures. Thus, the absorption coefficients which can be suitable for great performance optical modulators and multiple infrared optical device applications can be easily obtained by tuning the external electric field value and the Al concentration at the well center.

Effects of applied electric and magnetic fields on the nonlinear optical properties of asymmetric [formula omitted] double inverse parabolic quantum well

The combined effects of electric and magnetic fields on the optical absorption coefficients and refractive index changes related to the intersubband transitions within the conduction band of asymmetric GaAs/Ga1-xAlxAs double inverse parabolic quantum wells are studied using the effective-mass approximation and the compact density-matrix approach. The results are presented as a function of the incident photon energy for the different values of the electromagnetic fields and the structure parameters such as quantum well width and the Al concentration at the well center. It is found that the optical absorption coefficients and the refractive index changes are strongly affected not only by the magnitudes of the electric and magnetic fields but also by the structure parameters of the system.

Optical Responses in Asymmetric Inverse Parabolic Quantum Wells: Effects of Laser Fields and Hydrostatic Pressure

Wells: E ects of Laser Fields and Hydrostatic Pressure M.E. Mora-Ramos, A.L. Morales and C.A. Duque Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, CP. 62209, Mexico Grupo de Materia Condensada-UdeA, Instituto de Fisica, Facultad de Ciencias Exactas y Naturales Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellin, Colombia Fisica Teorica y Aplicada, Escuela de Ingenieria de Antioquia, AA 7516, Medellin, Colombia

Nonlinear intersubband transitions in a parabolic and an inverse parabolic quantum well under applied magnetic field

In this study, both the intersubband optical absorption coefficients and the refractive index changes as dependent on the magnetic field are calculated in a parabolic (PQW) and an inverse parabolic quantum well (IPQW) for different Al concentrations at the well center. Our results show that the position and the magnitude of the linear, nonlinear and total absorption coefficients and refractive index changes depend on the magnetic field strength and the Al concentration at the well center. By decreasing the Al concentration at the well center we can obtain a red shift and a blue shift in the intersubband optical transitions for PQWs and IPQWs, respectively. Thus, the absorption coefficients and the refractive index changes which can be suitable for great performance optical modulators and multiple infrared optical device applications can be easily obtained by tuning the applicable magnetic field value and the Al concentration at the well center.

Electron states and related optical responses in asymmetric inverse parabolic quantum wells

The article reports the obtention of the conduction band energy states for electrons in a AlxGa1−x As-based quantum well with inverse parabolic confinement. Accordingly, it has been possible to calculate the intersubband electron-transition-related optical absorption and rectification coefficients. The comparison between the results in the cases of symmetric and asymmetric rectangular barrier configurations allows to verify the possibility of the second-order optical rectification in the asymmetric case as well as a rather drastic change in the absorption coefficient as a function of the height of the inverse parabolic potential in such a configuration.

Effects of applied electromagnetic fields on the linear and nonlinear optical properties in an inverse parabolic quantum well

In this present work, we have investigated theoretically the effects of applied electric and magnetic fields on the linear and nonlinear optical properties in a GaAs/AlxGa1−xAs inverse parabolic quantum well for different Al concentrations at the well center. The Al concentration at the barriers was always xmax=0.3. The energy levels and wave functions are calculated within the effective mass approximation and the envelope function approach. The analytical expressions of optical properties are obtained by using the compact density-matrix approach. The linear, third-order nonlinear and total absorption and refractive index changes depending on the Al concentration at the well center are investigated as a function of the incident photon energy for the different values of the applied electric and magnetic fields. The results show that the applied electric and magnetic fields have a great effect on these optical quantities.

Magneto-donors in laser-dressed inverse parabolic quantum wells

By using a nonperturbative theory within the effective mass approximation, the combined effects of the intense laser radiation and applied magnetic field on the shallow-donor binding energy in inverse parabolic quantum wells are investigated. It is found that: (i) the increasing of the laser intensity dramatically modifies the confinement potential shape leading to the formation of a multiple well potential within the structure; (ii) the binding energy as a function of the impurity position and external fields follows a similar behavior to that observed for the spatial distribution of the electron wave function; (iii) the peak positions in valence-to-donor-related absorption spectra can be tuned at specific energies by changing the external field strengths. Our results suggest that this profile could be used in designing new devices with properties controlled by laser and magnetic fields.

Linear and nonlinear optical absorption coefficients in inverse parabolic quantum wells under static external electric field

In the present theoretical study, the linear and third-order nonlinear optical absorption coefficients have been calculated in GaAs/Ga1−xAlxAs inverse parabolic quantum wells (single and double) subjected to an external electric field. Our calculations are based on the potential morphing method in the effective mass approximation. The systematic theoretical investigation contains results with all possible combinations of the involved parameters, as quantum well width, quantum barrier width, Al concentration at each well center and magnitude of the external electric field. Our results indicate that in most cases investigated, the increase of the electric field blue-shifts the peak positions of the total absorption coefficient. In all cases studied it became apparent that the incident optical intensity considerably affects the total absorption coefficient.

Interband absorption and exciton binding energy in an inverse parabolic quantum well under the magnetic field

We have investigated the effects of the magnetic field which is applied perpendicular to the growth direction of the well on the interband absorption and on the binding energy of the excitons in an GaAs / Ga 1 − x Al x As inverse parabolic quantum well (IPQW) with different widths as well as different Al concentrations at the well center. The calculations were performed within the effective mass approximation, using a variational method. We observe that IPQW structure turns into parabolic quantum well with the inversion effect of the magnetic field and the effective band gap of the system can be modified by changing Al concentration at the well center, the strength of the magnetic field and well dimensions. This case directly influences the nature of electronic and optical properties in this structure.

Density of impurity states of hydrogenic impurities in an inverse parabolic quantum well under the magnetic field

We investigated the effects of the magnetic field on the density of impurity states in a GaAs/GaAlAs inverse parabolic quantum well (IPQW) for different Al concentrations at the well center. The calculations were performed within the effective mass approximation, using a variational method. We report in this paper the effects of the magnetic field, well width and the Al concentration at the well center on the density of states and the binding energies of the donor impurities.

Binding energy of impurity states in an inverse parabolic quantum well under magnetic field

We have investigated the effects of the magnetic field which is directed perpendicular to the well on the binding energy of the hydrogenic impurities in an inverse parabolic quantum well (IPQW) with different widths as well as different Al concentrations at the well center. The Al concentration at the barriers was always x max = 0.3 . The calculations were performed within the effective mass approximation, using a variational method. We observe that IPQW structure turns into parabolic quantum well with the inversion effect of the magnetic field and donor impurity binding energy in IPQW strongly depends on the magnetic field, Al concentration at the well center and well dimensions.

Tight-binding calculation of electronic states in an inverse parabolic quantum well.

Tight-binding calculation of electronic states in an inverse parabolic quantum well.

Quantum Well Local-to-Global State Transitions under an Electric Field

Electric-field-induced optical effects have been studied in two-step and inverse parabolic quantum wells grown by molecular beam epitaxy. The inverse parabolic well was grown by digital and analog compositional grading techniques. Both types of wells had much larger Stark shifts than the conventional square well. This is an effect of the special shape of the well allowing local-to-global state transitions. Observed deviations from calculated results for the analog inverse parabolic well are attributed to fluctuation in quantum well parameters.

Inverse parabolic quantum well and its quantum-confined Stark effect

An inverse parabolic quantum well was successfully grown by molecular-beam epitaxy using a digital compositional grading superlattice composed of Al0.36Ga0.64As/GaAs. The photoluminescence and photocurrent measurements for this structure gave a good agreement between experimental and theoretical results. Large Stark shift and amplitude reduction of 1e-1hh exciton resonance under applied electric field were found in the photoluminescence spectra, which are substantially larger than the conventional square quantum well. These properties benefited from the concept of local-to-global state transitions.

Inverse parabolic quantum wells grown by molecular-beam epitaxy using digital and analog techniques.

An ${\mathrm{Al}}_{0.36}$${\mathrm{Ga}}_{0.64}$As/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As inverse parabolic quantum-well structure was grown by molecular-beam epitaxy using both digital and analog compositional grading techniques. Photoluminescence and photocurrent measurements showed distinct exciton peaks for both types of wells. A large Stark shift was found for the digital well, in agreement with the calculations. An observed deviation for the analog well was ascribed to fluctuation in quantum-well parameters. Finally, advantages and disadvantages of the two growth techniques are discussed.