Photoionization and binding energy of a donor impurity in a quantum dot under an electric field: Effects of the hydrostatic pressure and temperature

Using the perturbation approach, we have calculated the donor impurity related photoionization cross-section in a quantum dot under different temperature and hydrostatic pressure conditions. Our calculation have revealed the dependence of the photoionization cross-section on the confinement strength, temperature and hydrostatic pressure.     

Donor-impurity related binding energy and photoinization cross-section in quantum dots: electric and magnetic fields and hydrostatic pressure effects

We have studied the behavior of the binding energy and photoionization cross-section of a donor-impurity in cylindrical-shape GaAs-Ga_0.7Al_0.3As quantum dots, under the effects of hydrostatic pressure and in-growth direction applied electric and magnetic fields. We have used the variational method under the effective mass and parabolic band approximations. Parallel and perpendicular polarizations of the incident radiation and several values of the quantum dot geometry have also been considered. Our results show that the photoionization cross-section growths as the hydrostatic pressure is increased. For parallel polarization of the incident radiation, the photoionization cross-section decreases when the impurity is shifted from the center of the dot. In the case of perpendicular polarization of the incident radiation, the photoionization cross-section increases when the impurity is shifted in the radial direction of the dot. For on-axis impurities the transitions between the ground state of the impurity and the ground state of the quantum dot are forbidden. In the low pressure regime (less than 13.5 kbar) the impurity binding energy growths linearly with pressure, and in the high pressure regime (higher than 13.5 kbar) the binding energy growths up to a maximum and then decreases. Additionally, we have found that the applied electric and magnetic fields may favor the increase or decrease in binding energy, depending on the impurity position.     

Hydrostatic pressure and temperature dependence of correlation energy in a spherical quantum dot

The combined effects of hydrostatic pressure and temperature on the ground state binding energy of two electrons in a GaAs spherical quantum dot have been studied by using a perturbation approach within the effective-mass approximation. Our results show that an increment in temperature results in a decrease of the correlation energy while an increment in the pressure for the same temperature increases the correlation energy at a particular dot size. In all cases, it is observed that there is a decrease in the correlation energy due to an increase in the dot size with a given temperature and pressure. The combined effects of hydrostatic pressure and temperature affect the correlation energies appreciably for narrower dots only. The correlation contributes 10%–30% to the binding energy. All the calculations have been carried out with finite barriers, and good agreement is obtained with the existing literature values.     

Hydrostatic pressure and temperature effects of an exciton-donor complex in quantum dots

Using the matrix diagonalization method and the compact density-matrix approach, we studied the combined effects of hydrostatic pressure and temperature on the electronic and optical properties of an exciton-donor complex in a disc-shaped quantum dot. We have calculated the binding energy and the oscillator strength of the intersubband transition from the ground state into the first excited state as a function of the dot radius. Based on the computed energies and wave functions, the linear, third-order nonlinear and total optical absorption coefficients as well as the refractive index have been examined. We find that the ground state binding energy and the oscillator strength are strongly affected by the quantum dot radius, hydrostatic pressure and temperature. The results also show that the linear, third-order nonlinear and total absorption coefficients and refractive index changes strongly depend on temperature and hydrostatic pressure.     

The effects of temperature and hydrostatic pressure on the photoionization cross-section and binding energy of shallow donor impurities in quantum dots

Using a variational approach, we have calculated the hydrostatic pressure and temperature effects on the donor impurity related photoionization cross-section and impurity binding in GaAs/GaAlAs quantum dots. Our calculations have revealed the dependence of the photoionizaton cross-section and the impurity binding on temperature and hydrostatic pressure.     

压力下GaN/Ga1-xAlxN量子点中杂质态的界面效应

考虑界面处导带弯曲,流体静压力以及有效质量随量子点位置的依赖性,采用变分法以及简化相干势近似,研究了无限高势垒GaN/Ga_1-xAl_xN球形量子点中杂质态的界面效应,计算了杂质态结合能随量子点尺寸、电子面密度以及压力的变化关系。结果表明,结合能随压力的增大呈线性增加的趋势,有效质量位置的依赖性以及导带弯曲对结合能有不容忽视的影响。     

Effect of various factors on binding energy of pyramid quantum dot: pressure,temperature and impurity position

In the present work, we have studied the effects of hydrostatic pressure, temperature and impurity position on the donor binding energy of a pyramid quantum dot. For this goal, using variational method, we have calculated the binding energy as a function of dot size for various impurity locations, different pressures and temperatures. According to the results, we have found that the binding energy increases when the pressure increases and it enhances as the temperature decreases. Our results show that these effects play an important and considerable role on the donor binding energy of a pyramid quantum dot.     

Combined effects of hydrostatic pressure and temperature on nonlinear properties of an exciton in a spherical quantum dot under the applied electric field

Within the framework of the effective-mass approximation, we have calculated the combined effects of hydrostatic pressure, temperature and applied electric field on an exciton confined in a typical GaAs/Ga_0.7Al_0.3As quantum dot. Several inputs of the confinement potential, hydrostatic pressure, temperature, and applied electric field have been considered. Our findings suggest that (1) the effect of the confinement strength is dominant over the electric field effect, (2) the oscillator strength is an increasing function of the hydrostatic pressure, (3) the absorption coefficients and energy difference depend strongly on the hydrostatic pressure but weakly on the temperature, (4) the absorption coefficients with considering excitonic effects are stronger than those without considering excitonic effects and the absorption peak will move to the right side induced by the electron-hole interaction, (5) the applied electric field may effect either the size or the position of absorption peaks of excitons.     

Effects of hydrostatic pressure on the donor impurity in a cylindrical quantum dot with Morse confining potential

The effects of hydrostatic pressure and size quantization on the binding energies of a hydrogen-like donor impurity in cylindrical GaAs quantum dot (QD) with Morse confining potential are studied using the variational method and effective-mass approximation. In the cylindrical QD, the effect of hydrostatic pressure on the binding energy of electron has been investigated and it has been found that the application of the hydrostatic pressure leads to the blue shift. The dependence of the absorption edge on geometrical parameters of cylindrical QD is obtained. Selection rules are revealed for transitions between levels with different quantum numbers. It is shown that for the radial quantum number, transitions are allowed between the levels with the same quantum numbers, and any transitions between different levels are allowed for the principal quantum number.     

纤锌矿GaN/AlxGa1-xN应变柱形量子点中杂质态结合能及其压力效应

考虑应变及流体静压力,在有效质量近似下,利用变分法计算了无限高GaN/Al<,x>Ga<,1-x>N应变柱形量子点中类氢杂质结合能.结果表明,在量子点尺寸较小情况下,应变增加了杂质态结合能;而在量子点尺寸较大情况下,应变降低了杂质态结合能.随着Al摩尔分数的增加,杂质态结合能减小.杂质态结合能随着流体静压力的增加而增大...     

Pressure-induced threshold optical pump intensity in a CdTe/ZnTe quantum dot

Pressure-induced binding energies of an exciton and a biexciton are studied taking into account the geometrical confinement effect in a CdTe/ZnTe quantum dot. Coulomb interaction energy is obtained using Hartree potential. The energy eigenvalue and wave functions of exciton and the biexciton are obtained using the self-consistent technique. The effective mass approximation and BenDaniel-Duke boundary conditions are used in the self-consistent calculations. The pressure-induced nonlinear optical absorption coefficients for the heavy hole exciton and the biexciton as a function of incident photon energy for CdTe/ZnTe quantum dot are investigated. The optical gain coefficient with the injection current density, in the presence of various hydrostatic pressure values, is studied in a CdTe/ZnTe spherical quantum dot. The pressure-induced threshold optical pump intensity with the dot radius is investigated. The results show that the pressure-induced electronic and optical properties strongly depend on the spatial confinement effect.     

Pressure effects on the donor binding energy in zinc-blende InGaN/GaN quantum dot

Based on the effective-mass approximation, the hydrostatic pressure effects on the donor binding energy of the hydrogenic impurity in zinc-blende (ZB) InGaN/GaN quantum dot (QD) are investigated by means of a variational procedure. Numerical results show that the donor binding energy increases when the hydrostatic pressure increases for any impurity position and QD structure parameter. Moreover, it is found that the hydrostatic pressure has a remarkable influence on the donor binding energy of the hydrogenic impurity located at the vicinity of dot center in ZB InGaN/GaN QD.     

Hydrostatic pressure effects on exciton states in InAs/GaAs quantum dots

Based on the effective-mass approximation, the hydrostatic pressure effects on exciton states in InAs/GaAs self-assembled quantum dots (QDs) are studied by means of a variational method. Numerical results show that the exciton binding energy has a minimum with increasing dot height for any hydrostatic pressure. The interband emission energy increases when the hydrostatic pressure increases. In particular, we find that hydrostatic pressure has a remarkable effect on exciton states for small QD size. Our results are in agreement with experiment measurements.     

The effects of temperature and hydrostatic pressure on the photoionization cross-section and binding energy of impurities in quantum-well wires

Using a variational approach, we have calculated the donor impurity related photoionization cross-section and impurity binding in GaAs/GaAlAs quantum-well wires under different temperature and hydrostatic pressure conditions. Our calculation have revealed the dependence of the photoionization cross-section and the impurity binding on temperature and hydrostatic pressure.     

Effects of electric field and hydrostatic pressure on donor binding energies in a spherical quantum dot

The binding energies of a hydrogenic donor in a GaAs spherical quantum dot in the Ga_1−xAl_xAs matrix are presented assuming parabolic confinement. Effects of hydrostatic pressure and electric field are discussed on the results obtained using a variational method. Effects of the spatial variation of the dielectric screening and the effective mass mismatch are also investigated. Our results show that (i) the ionization energy decreases with dot size, with the screening function giving uniformly larger values for dots which are less than about 25 nm, (ii) the hydrostatic pressure increases the donor ionization energy such that the variation is larger for a smaller dot, and (iii) the ionization energy decreases in an electric field. All the calculations have been carried out with finite barriers and good agreement is obtained with the results available in the literature in limiting cases.     

Impurity-related polarizability and photoionization-cross section in double quantum wells under electric fields and hydrostatic pressure

Double quantum well heterostructures are quite important for the exploration of correlated electron states in two-dimensional systems. By using the variational procedure, within the effective-mass and parabolic-band approximations, the effects of both electric field and hydrostatic pressure on the shallow-donor-impurity related polarizability and photoionization cross-section in GaAs–Ga_1−xAl_xAs double asymmetric quantum wells are presented. The electric field is considered to be applied along the growth direction. It is found that the impurity binding energy and polarizability can be tuned by means of an applied external electric field or hydrostatic pressure in asymmetric double quantum wells, a behavior which could be used in the design and construction of semiconductor devices. The photoionization cross-section magnitude increases as the pressure and applied electric field are increased, except beyond the Γ–X crossover in the barrier material, where a decrease of the photoionization cross-section is expected due the smaller confinement of the impurity wave function.     

Hydrostatic pressure effects on impurity states in InAs/GaAs quantum dot

Within the framework of effective-mass approximation, the hydrostatic pressure effects on the donor binding energy of a hydrogenic impurity in InAs/GaAs self-assembled quantum dot(QD) are investigated by means of a variational method. Numerical results show that the donor binding energy increases when the hydrostatic pressure increases for any impurity position and QD size. Moreover, the hydrostatic pressure has a remarkable influence on the donor binding energy for small QD. Realistic cases, including the impurity in the QD and the surrounding barrier, are considered.     

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_xGa_1−xAs 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.     

Hydrostatic pressure and temperature effects on the electronic energy levels of a spherical quantum dot placed at the center of a nano-wire

The effect of pressure and temperature on the electronic structure of an InAs spherical quantum dot located at the center of a GaAs cylindrical nano-wire have been determined using finite element method, within the effective mass approximation. The energy levels and transition energies are numerically calculated as a function of the dot radius, pressure and temperature. It is shown that the pressure and temperature effects are significant and should be considered in the study of low-dimensional semiconducting systems. The results show that; energy levels (i) decrease as the dot radius increases (ii) decrease as the pressure increases and (iii) increase as the temperature increases. For very small dot radii, the energy levels show unusual behavior, such that the energy levels increase as the pressure increases. We also found that the transition energy (i) increases as the dot size decreases (ii) increases as the pressure increases and (iii) decreases as the temperature increases.     

The hydrostatic pressure and electric field effects on the normalized binding energy of hydrogenic impurity in a GaAs/AlAs spherical quantum dot

A theoretical study of combined effects of the hydrostatic pressure and the electric field on the subband ground state energy and on the normalized ground state binding energy of a hydrogenic donor impurity on center located in a GaAs/AlAs spherical quantum dot with fixed dot radius is presented. The study is performed in the framework of the effective mass and parabolic band approximations and using a variational procedure. As a key result, it may be possible to gather high resolution maps of electric field on the studied structure with described technique.