Effect Of Conduction Band Non-parabolicity Research Articles

Simultaneous Effects of External Electric Field and Conduction Band Nonparabolicity on Optical Properties of a GaAs Quantum Dot Embedded at the Center of a GaAlAs Nano-Wire

An investigation of the optical properties of a GaAs spherical quantum dot which is located at the center of a Ga1−xAlxAs cylindrical nano-wire has been performed in the presence of an external electric held. The band nonparabolicity effect is also considered using the energy dependent effective mass approximation. The energy eigenvalues and corresponding wave functions are calculated by finite difference approximation and the reliability of calculated wave functions is checked by computing orthogonality. Using computed energy eigenvalues and wave functions, the linear, third-order nonlinear and total optical absorption coefficients and refractive index changes are examined in detail. It is found that (i) Presence of electric field causes both blue and red shifts in absorption spectrum; (ii) The absorption coefficients shift toward lower energies by taking into account the conduction band nonparabolicity; (iii) For large values of electric field the effect of conduction band nonparabolicity is less dominant and parabolic band is estimated correctly; (iv) In the presence of electric field and conduction band nonparabolicity the nonlinear term of absorption coefficient rapidly increases by increasing incident optical intensity. In other words, the saturation in optical spectrum occurs at lower incident optical intensities.

Numerical Investigation of the Effects of Conduction Band Nonparabolicity on the Conduction Sub-band Dispersion Relationships in a Al0.88In0.12N/Ga0.9

Numerical Investigation of the Effects of Conduction Band Nonparabolicity on the Conduction Sub-band Dispersion Relationships in a Al0.88In0.12N/Ga0.9

Effect of conduction band nonparabolicity on the optical properties in a single quantum well under hydrostatic pressure and electric field

The effect of conduction band nonparabolicity on the linear and nonlinear optical properties such as absorption coefficients, and changes in the refractive index are calculated in the Al0.3Ga0.7As/GaAs heterostructure-based symmetric rectangular quantum well under applied hydrostatic pressure and electric field. The electron envelope functions and energies are calculated in the effective mass equation including the conduction band nonparabolicity. The linear and nonlinear optical properties have been calculated in the density matrix formalism with two-level approximation. The conduction band nonparabolicity shifts the positions of the optical properties and decreases their strength compared to those without this correction. Both the optical properties are enhanced with the applied hydrostatic pressure. While the absorption coefficients are bleached under the combined effect of high pressure and electric field, the bleaching effect is reduced when nonparabolicity is included.

Effect of conduction band non-parabolicity on the donor states in zinc-blende GaN/AlGaN quantum dot

Donor binding energies of a hydrogenic impurity in a zinc-blende (ZB) GaN/AlxGa1–xN quantum dot are investigated. We have applied the variational method using 1s-hydrogenic wave-function in the framework of the single band effective mass approximation with two-parametric wave-function. The barrier height and the mass variation of AlGaN barrier are found out for different Al content in the dot. The calculations have been carried out with the inclusion of conduction band non-parabolicity using the Luttinger-Kohn model which introduces additional energy in the Hamiltonian. The numerical results show that the: 1 binding energy increases as the dot radius decreases for all Al content 2 binding energy increases with the Al content for all the dot radii 3 the inclusion of non-parabolic effects leads to more binding for all the values of dot radius and is significant for narrow wells. These results are compared with the other existing available literature.

External electric field, hydrostatic pressure and conduction band non-parabolicity effects on the binding energy and the diamagnetic susceptibility of a hydrogenic impurity quantum dot

Electric field, hydrostatic pressure and conduction band non-parabolicity effects on the binding energies of the lower-lying states and the diamagnetic susceptibility of an on-center hydrogenic impurity confined in a typical GaAs / Al x Ga 1 − x As spherical quantum dot is theoretically investigated, by direct diagonalization of the Hamiltonian. To this end, the effect of band non-parabolicity has been performed, by means of the Luttinger–Kohn effective mass equation. Binding energies and diamagnetic susceptibility of the hydrogenic impurity are computed as a function of the dot size, external electric field strength and hydrostatic pressure, with considering the edge-band non-parabolicity. Results show that the external electric field and the hydrostatic pressure have an obvious influence on the binding energies and the diamagnetic susceptibility of the impurity.

Simultaneous Effects of Hydrostatic Pressure and Conduction Band Non-parabolicity on Binding Energies and Diamagnetic Susceptibility of a Hydrogenic Impurity in Spherical Quantum Dots

Simultaneous effects of conduction band non-parabolicity and hydrostatic pressure on the binding energies of 1S, 2S, and 2P states along with diamagnetic susceptibility of an on-center hydrogenic impurity confined in typical GaAs/AlxGa1−xAs spherical quantum dots are theoretically investigated using the matrix diagonalization method. In this regard, the effect of band non-parabolicity has been performed using the Luttinger—Kohn effective mass equation. The binding energies and the diamagnetic susceptibility of the hydrogenic impurity are computed as a function of the dot radius and different values of the pressure in the presence of conduction band non-parabolicity effect. The results we arrived at are as follows: the incorporation of the band edge non-parabolicity increases the binding energies and decreases the absolute value of the diamagnetic susceptibility for a given pressure and radius; the binding energies increase and the magnitude of the diamagnetic susceptibility reduces with increasing pressure.

Conduction band non-parabolicity effect on the binding energy and the diamagnetic susceptibility of an on-center hydrogenic impurity in spherical quantum dots

Energy eigenvalues, binding energy and diamagnetic susceptibility of an on-center hydrogenic impurity confined in typical GaAs/Al x Ga 1− x As spherical quantum dots are theoretically investigated, using the matrix diagonalization method. In this regard, the effect of band non-parabolicity has been performed, by means of the Luttinger–Kohn effective mass equation. The lower-lying states, the binding energy and the diamagnetic susceptibility of the hydrogenic impurity are computed as a function of the dot size, with and without conduction band non-parabolicity effect. Results show that the band edge non-parabolicity considerably changes the electronic structure, the binding energy and the diamagnetic susceptibility, especially at small radii.

Conduction band non-parabolicity effect on the optical absorption coefficient and refractive index changes of spherical quantum dots

Optical absorption coefficients and refractive index changes associated with intersubband transition in typical GaAs / Al x Ga 1 − x As spherical quantum dots are theoretically investigated, both in the presence and in the absence of the conduction band non-parabolicity effect. In this regard, the effect of band non-parabolicity on the eigenvalues and eigenfunctions of the dot has been performed using the Luttinger–Kohn effective mass equation. Also, by means of the compact-density-matrix approach the linear and nonlinear optical absorption coefficients and refractive index changes have been calculated. The results show that magnitudes of these quantities are decreased and the peaks are shifted to the lower energies as the influence of band non-parabolicity is considered.

Hydrostatic pressure and conduction band non-parabolicity effects on the impurity binding energy in a spherical quantum dot

The binding energy of a shallow hydrogenic impurity in a spherical quantum dot under hydrostatic pressure with square well potential is calculated using a variational approach within the effective mass approximation. The effect of conduction band non-parabolicity on these energies is also estimated. The binding energy is computed for GaAs spherical quantum dot as a function of dot size, hydrostatic pressure both in the presence and absence of the band non-parabolicity effect. Our results show that (i) the hydrostatic pressure increases the impurity binding energy when dot radius increases for a given pressure, (ii) the hydrostatic pressure with the band non-parabolicity effect effectively increases the binding energy such that the variation is large for smaller dots and (iii) the maximum contribution by the non-parabolicity effect is about 15% for narrow dots. Our results are in good agreement with Perez-Merchancano et al. [J. Phys. Condens. Matter 19 (2007) 026225] who have not considered the conduction band non-parabolicity effect.

Quantum confinement effect on the effective mass in two-dimensional electron gas of AlGaN/GaN heterostructures

We report the results of direct measurements and a theoretical investigation of the in-plane effective mass in the two-dimensional electron gas of nominally undoped AlGaN/GaN heterostructures with a different degree of quantum confinement. It is shown that in most cases the conduction band nonparabolicity effect is overestimated and the electron wave-function penetration into the barrier layer should be taken into account. The contribution of the wave-function hybridization is determined to play the dominant role. The band edge effective mass value is deduced to be (0.2±0.01)m0.

Refractive index of Si-doped n-InGaAs

The dependence of the refractive index of Si-doped n-InGaAs on carrier density was investigated. The shift in the refractive index from that of undoped InGaAs was found to be mainly caused by the band-filling effect, the band-gap shrinkage effect, and the plasma effect. Model calculations agreed better with the measured data when the conduction band nonparabolicity effect was taken into account. Nevertheless, the calculated refractive index values were slightly lower than the experimental values. Because the difference was larger for photon energies close to the band-gap energy of InGaAs, the shift in the refractive index is attributed to the absorption tail effect that appears near the band-gap energy due to Si doping.

Effect of conduction band nonparabolicity on the dark current in a quantum well infrared detector

Taking into account electron scattering with confined plasmon-phonon coupled modes in a many-body formalism, the dark currents in a quantum well structure based on the Al0.27Ga0.73As∕GaAs heterojunctions have been calculated The nonparabolicity of the conduction band, finite temperature, and applied bias has been included in the calculation of the scattering rates. Good agreement with the experiments has been obtained by the inclusion of the nonparabolicity of the conduction band in the theory.

Effect of conduction band non-parabolicity on the donor states in GaAs–(Al,Ga)As spherical quantum dots

The binding energy of a shallow, hydrogenic on-centre impurity in a GaAs–Al x Ga 1− x As quantum dot is calculated using the standard variational technique. The effect of band non-parabolicity is considered using the Luttinger–Kohn ‘effective mass’ equation. The electronic energy level and the donor binding energy are computed as a function of the dot size, both in the presence and in absence of the band non-parabolicity effect. Results indicate noticeable differences in two cases, especially for small dots.

Atomistic Approach for Nanoscale Devices at the Scaling Limit and Beyond– Valley Splitting in Si

Band-structure effects on channel carrier density in the ultrathin-body end of the ITRS roadmap silicon (100) n-type metal oxide semiconductor field effect transistors (MOSFETs) are assessed here using a semi-empirical nearest-neighbor sp3d5s* tight-binding model with spin-orbit interaction. The calculations focus on the body thickness range between 10 and 18 atomic layers (∼1.5–2.5 nm). At this range, the standard effective mass approach is limited by its inability to capture the conduction band nonparabolicity effects and the subband splitting. The tight-binding simulations show interesting effects of ground-state subband splitting in this thickness range, and as a result of this, the channel charge density was found to fluctuate by as much as 30%. Additionally, it was observed that strict process tolerance is necessary in this thickness range in order to maintain an acceptable threshold voltage variation.

Study of Electron Transport in SOI MOSFETs Using Monte Carlo Technique with Full-Band Modeling

Effects of conduction-band non-parabolicity on electron transport properties in silicon-on-insulator (SOI) metal-oxide-semiconductor field effect transistors (MOSFETs) are studied by performing Monte Carlo simulation with a full-band modeling. An empirical pseudo-potential method is adopted for evaluating the two-dimensional electronic states in SOI MOSFETs. SOI-film thickness dependence of phonon-limited mobility, drift-velocity and subband occupancy is calculated and the results are compared with those of a simple effective mass approximation. The non-parabolicity effects are found to play an important role in 4-fold valleys under higher applied electric fields or at higher temperatures.

Influences of conduction band non-parabolicity on intersubband absorption and photon drag in a single quantum well

On the basis of a microscopic nonlocal theory and k· p approach, an analysis of conduction band non-parabolicity effects on the linear absorption and photon drag arising from intersubband transitions in a single quantum well has been carried out. It is shown via detailed numerical simulations that, in comparison with the non-parabolic band model, the parabolic model overestimates intersubband absorption and photon drag current; blueshifts of the absorption peak and zero crossing of photon drag current are also overestimated.

Some effects of conduction band nonparabolicity on electron reflection spectrum of multiquantum barriers

The effect of nonparabolicity of conduction band on the electron reflection spectrum of multiquantum barriers (MQB) has been examined. Drastic reduction in the effective barrier height is expected by adopting the nonparabolic model on the MQB which had been designed using the parabolic model for 1.5 μm semiconductor lasers (LDs). The predicted enhancement in barrier height by the MQB is over 600 meV under parabolic model. However, it decreases to 40 meV under nonparabolic model with the same structure. On the other hand, the experimental enhancement in barrier height by the MQB is estimated to be around 30 meV on 1.5 μm LDs, close to the value calculated by nonparabolic model. Those results suggest that a much higher effective barrier height can be realized by optimizing the MQB design taking the nonparabolicity into account. The conduction band nonparabolicity was incorporated by the k⋅p perturbation method.

Simplified treatment of many-body effects in the intersubband absorption of symmetric uniformly doped quantum wells at zero temperature

We present a simplified calculation of the intersubband absorption in symmetric, uniformly doped quantum wells at zero temperature, which takes into account conduction-band nonparabolicity (via an energy-dependent effective mass) and treats all effects (including the direct Coulomb, exchange, depolarization, and excitonlike) on an equal footing. There is no need to solve self-consistent equations (i.e., Hartree or Hartree-Fock) in our method and we obtain our results without recourse to advanced many-body techniques; yet we still find good agreement with experiments. We examine in particular the effect of conduction-band nonparabolicity on the peak absorption energy. Our results should therefore be of particular interest to experimentalists seeking to model their results.

Radiative interaction and disorder effect in the linear optical response of a multiple-quantum-well structure

Using a nonlocal local-field formalism, we show that, for a multiple-quantum-well (MQW) structure with well-width fluctuations, and in an internal-reflection configuration, the linear optical intersubband absorption spectra including peak positions and line shapes are strongly dependent on the number of quantum wells (QW's) in the structure and of the spatial distribution of the QW's. It is also demonstrated that an inclusion of the barrier-medium--vacuum interface enhances the electromagnetic coupling among QW's, and consequently leads to a significant modification of the optical-absorption spectra. By varying the intersubband relaxation time, we find that the local-field effect may substantially reduce the linewidth broadening arising from the conduction band nonparabolicity effect for a highly doped MQW system. This is in agreement with a previous prediction for a single QW. In addition, the present nonlocal theory is compared with the effective-medium theory (EMT). Our calculations show that the nonlocal effect in the optical response of QW's gives rise to a notable blueshift of the absorption peak compared to the results in the EMT approach. When the QW number is varied, the line shapes predicted from the two theories are also somewhat different.

Observation of double cyclotron resonance in modulation-δ-doped In0.52Al0.48As/In0.53Ga0.47As heterostructure by optical detection

We report an investigation of optical and electronic properties of a two-subband populated electron gas confined at a δ-doped Al0.48In0.52As/Ga0.47In0.53As heterostructure by the technique of far-infrared optically detected cyclotron resonance (ODCR). Oscillatory characteristics are observed in the ODCR spectrum, and interpreted in terms of the crossing between the Landau levels of the two-dimensional electron gas and the Fermi level from which the electron concentration and effective mass of the first and second subbands can be determined. Quite different effective masses associated with these subbands are obtained, reflecting the strong effects of conduction band nonparabolicity as well as polaron coupling in Ga0.47In0.53As quantum well.