Donor Binding Energy in GaAs/Ga1-x AlxAs Quantum Well: the Laser Field and Temperature Effects

Based on the effective-mass approximation theory and variational method, the laser field and temperature effects on the ground-state donor binding energy in the GaAs/Ga_1-xAl_xAs quantum well (QW) are investigated. Numerical results show that the donor binding energy depends on the impurity position, laser parameter, temperature, Al composition, and well width. The donor binding energy is decreased when the laser field and temperature are increased in the QW for any impurity position and QW parameter case. Moreover, the laser field has an obvious influence on the donor binding energy of impurity located at the vicinity of the QW center. In addition, our results also show that the donor binding energy decreases (or increases) as the well width (or Al composition x) increases in the QW.     

Donor impurity states in zinc-blende GaN/AlGaN quantum well: Quantum confinement and laser-dressed effects

Within the framework of effective-mass approximation, the effects of a laser field on the ground-state donor binding energy in zinc-blende (ZB) GaN/AlGaN quantum well (QW) have been investigated variationally. Numerical results show that the donor binding energy is highly dependent on QW structure parameters and Al composition in ZB GaN/AlGaN QW. The laser field effects are more noticeable on the donor binding energy of an impurity localized inside the QW with small well width and low Al composition. However, for the impurity located in the vicinity of the well edge of the QW, the donor binding energy is insensible to the variation of Al composition, well width and laser field intensity in ZB GaN/AlGaN QW. In particular, the competition effects between laser field and quantum confinement on impurity states have also been investigated in this paper.     

Donor impurity states in direct-gap SiGe quantum well: Applied electric field and quantum size effects

Within the framework of the effective-mass approximation and variational procedure, competition effects between applied electric field and quantum size on donor impurity states in the direct-gap Ge/SiGe quantum well (QW) have been investigated theoretically. Numerical results show that the applied electric field (quantum size) dominates electron and impurity states in direct-gap Ge/SiGe QW with large (small) well width. Moreover, the competition effects also induce that the donor binding energies show obviously different behaviors with respect to electric field in the QW with different well widths. In particular, when the impurity is located at left boundary of the QW, the donor binding energy is insensitive to the variation of well width when well width is large for any electric field case.     

Effects of laser field and electric field on impurity states in zinc-blende GaN/AlGaN quantum well

Based on the effective-mass approximation, the competition effects between the laser field and applied electric field on impurity states have been investigated variationally in the ZB GaN/AlGaN quantum well (QW). Numerical results show that for any laser field, the electric field makes the donor binding energy present asymmetric distribution with respect to the center of the QW. Moreover, when the laser field is weak, the electric field effects are obvious on the donor binding energy; however, the electric field effects are insensitive to the variation of donor binding energy in the ZB GaN/AlGaN QW with strong laser field.     

The effect of laser field intensity on polarizability in a quantum well

A systematic study of binding energy of the ground state of a hydrogenic donor in a quantum well is calculated in the presence of a uniform electric field for different measure of laser intensities. Binding energy of the ground state of a donor is calculated, within the effective mass approximation, with the Bessel and Airy functions. Polarizability of a laser dressed donor impurity in the presence of electric field is reported. It is observed that the polarizability (i) increases as intensity of the laser field increases (ii) increases with the electric field strength and (iii) increases drastically when both the fields are applied. The dependence of the donor binding energy on the well width, the laser field intensity and the electric field is discussed. Our results are in good agreement with the previous investigations for other heterostructures in the presence of laser intensity.     

Hydrostatic pressure effect on the donor impurity states in asymmetric multiple quantum wells

Based on the effective-mass approximation, hydrostatic pressure effect on the donor binding energy in zinc blende (ZB) InGaN/GaN asymmetric multiple quantum wells (AMQWs) is investigated variationally. Numerical results show that the hydrostatic pressure increases the donor binding energy for any impurity position. Moreover, the hydrostatic pressure effect is more noticeable if the impurity is localized inside the wide well of the AMQWs. For any hydrostatic pressure, the donor binding energy is distributed asymmetrically with respect to the center of the AMQWs. In particular, the donor binding energy of impurity located at the center of the wide well of the AMQWs is insensitive to the increment of the inter-well barrier width if the inter-well barrier width is large.     

纤锌矿GaN柱形量子点中类氢施主杂质态

在有效质量近似和变分原理的基础上,选取含两个变分参数的波函数,研究了纤锌矿结构的GaN/AlxGa1-xN单量子点中类氢施主杂质体系的结合能随量子点(QD)尺寸以及杂质在量子点中位置的变化,并与以前使用不同尝试波函数的计算结果进行了比较。结果表明:由我们选取的两变分参数波函数得到的结果与前人选取的两变分参数波函数得到的结果相比有所改进,而与选取一个变分参数波函数得到的结果一致。同时我们还计算了体系的维里定理值随量子点半径的变化情况,所得结果与前人工作结果一致,说明本文选取的两变分参数波函数能很好地描述柱形量子点中施主杂质态的运动。     

Simultaneous effects of hydrostatic pressure and applied electric field on the impurity-related self-polarization in GaAs/Ga1−xAlxAs multiple quantum wells

A detailed theoretical study of the combined effects of hydrostatic pressure and in-growth direction applied electric field on the binding energy and self-polarization of a donor impurity in a system of GaAs-(Ga,Al)As coupled square quantum wells is presented. The study is performed in the framework of the effective mass and parabolic band approximations and using a variational procedure. The electron effective mass, the dielectric constant, the barrier height, the well sizes, all them varying with the hydrostatic pressure are taken into account within the study. The results obtained show that the impurity binding energy and its self-polarization bear strong dependencies with the hydrostatic pressure, the strength of the applied electric field, the width of the confining potential barriers, and the impurity position.     

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.     

Lateral electric field effects on quantum size confinement in cylindrical quantum dot under parabolic potential

Within the effective mass approximation, we investigated theoretically the ground-state energy of a single particle and the binding energy of the neutral donor impurity (D⁰) affected by a lateral electric field in a parabolic quantum dot (QD). The results show that the electron and the hole ground-state energy and the band to band transition energies shift to lower values (red shift) by increasing the field intensity. The quantum Stark shift (QSS) for the electron increases rapidly in the quasi spherical QD (QSQD) by increasing the lateral field, whereas for the hole it increases monotony. In the cylindrical QDs (CQDs), we found that the QSS for electron and hole increase monotonically. The quantum size, lateral electric field and impurity position effect on the binding energy of neutral donor (D⁰) is studied. Unexpected behavior of D⁰ in quantum well limit (QW), the binding energy of D⁰ is increasing (blue shift) with increasing QD radius R$R$ at the presence of a lateral electric field. It appears that for a fixed size of the QD, the off-center binding energy decreases when the impurity ion is displaced from the center to the QD borders, while it is shifted to lower energy with increasing the field.     

应变纤锌矿GaN/AlxGa1-xN柱形量子点中类氢施主杂质态结合能的压力效应

考虑应变,在有效质量、有限高势垒近似下,变分研究了纤锌矿GaN/AlxGa1-xN柱形量子点中类氢施主杂质态结合能随流体静压力、杂质位置及量子点结构参数(量子点高度、半径、Al含量)的变化关系．结果表明,类氢施主杂质态结合能随流体静压力增大而增大,且在量子点尺寸较小时,流体静压力对杂质态结合能的影响更为显著．受流体静压力的影响,杂质态结合能随量子点高度、半径的增加而单调减少,且变化趋势加剧;随Al含量增加而增大的趋势变缓．无论是否施加流体静压力,随着类氢施主杂质从量子点左界面沿材料生长方向移至右界面,杂质态结合能在量子点的右半部分存在一极大值．流体静压力使得极大值点向量子点中心偏移．     

Diamagnetic susceptibility of a laser dressed donor in a quantum well

The binding energy of laser dressed donor impurity is calculated under the influence of a magnetic field in a quantum well. The binding energy of the ground state of a donor is investigated, within the single band effective mass approximation, variationally for different concentrations at the well centre. The effect of laser and magnetic fields on diamagnetic susceptibility of the hydrogenic donor is reported. The Landau energy levels of electrons in the quantum well as a function of magnetic field are reported. The results show that the diamagnetic susceptibility (i) decreases drastically as intensity of the laser field increases (ii) increases with the magnetic field strength (iii) decreases as the Al-concentration decreases and (iv) a variation of increase in binding energy is observed when non-parabolicity is included and this effect is predominant for narrow wells. Our results are in good agreement with previous investigations for other heterostructures in the presence of laser intensity.     

Density of impurity states of shallow donors in a quantum well under intense laser field

The density of donor impurity states in a square GaAs–AlGaAs quantum well under an intense laser field is calculated taking into account the laser dressing effects on both the Coulomb potential and the confining potential. Using the effective-mass approximation within a variational scheme, the donor binding energy is obtained as a function of the laser dressing parameter, and the impurity position. Our results point out that a proper consideration of the density of impurity states may be of relevance in the interpretation of the optical phenomena related to shallow impurities in quantum wells, where the effects of an intense laser field compete with the quantum confinement.     

Calculation of Binding Energies of the Ground and Excited States of a Donor in GaAs-A1xGal-xAs Step Quantum Wells

In this paper we present for the first time completely analytical variational expressions for calculating the binding energies of the low-lying bound states of a hydrogenic donor in a quantum well (QW). These expressions can be used for the problem of the binding energy of an impurity in a general manner, e.g. for calculating the binding energies of a donor associated with subband states of any order in the QW with any arbitrary potential profile. 70 demonstrate the utilization of these expressions we have theoretically studied the binding energies for the ground and a few low-lying excited etates of a hydrogenic donor in a stepped quantam well (SQW). The variations of the binding energies for these donor etates with impurity positions are investigated for different heights of the step potential. The numerical calculation results show that the binding-energy curves in the SQW, in contrast to the case of the flat quantum wells (FQW's), exhibit a non-symmetrical structure relative to the center of the QW and depend on the sub-barrier potential. The peak position in the binding energy curves shifts away from the region occupied by the sub-barrier as increasing sub-barrier height. The maximum in the binding energies increases as the step potential increaaes. These effects can be interpreted by referring to the variation of the electron probability-density distribution and of the lowest subband in the SQW. The shape of the binding-energy curves related to the 2po-like state is different from the other states. It is associated with the particular feature of the wave function of the 2po state in the QW.     

Comparison of external electric and magnetic fields effect on binding energy of hydrogenic donor impurity in different shaped quantum wells

The effects of external electric and magnetic fields on the ground state binding energy of hydrogenic donor impurity are compared in square, V-shaped, and parabolic quantum wells. With the effective-mass envelope-function approximation theory, the ground state binding energies of hydrogenic donor impurity in InGaAsP/InP QWs are calculated through the plane wave basis method. The results indicate that as the quantum well width increases, the binding energy changes most fast in SQW. When the well width is fixed, the binding energy is the largest in VQW for the donor impurity located near the center of QWs. For the smaller and larger well width, the electric field effect on binding energy is the most significant in VQW and SQW, respectively. The magnetic field effect on binding energy is the most significant in VQW. The combined effects of electric and magnetic fields on the binding energy of hydrogenic donor impurity are qualitative consistent in different shaped QWs.     

Simultaneous effects of temperature and pressure on the donor binding energy in a V-groove quantum wire

The influence of temperature and pressure, simultaneously, on the binding energy of a hydrogenic donor impurity in a ridge GaAs/Ga_1−xAl_xAs quantum wire is studied using a variational procedure within the effective mass approximation. The subband energy and the binding energy of the donor impurity in its ground state as a function of the wire bend width and impurity location at different temperatures and pressures are calculated. The results show that, when the temperature increases, the donor binding energy decreases for a constant applied pressure for all wire bend widths. Also, the binding energy increases by increasing the pressure for a constant temperature for all wire bend widths. In addition, when the temperature and pressure are applied simultaneously the binding energy decreases as the quantum wire bend width increases. On the whole, it is deduced that the temperature and pressure have important effects on the donor binding energy in a V-groove quantum wire.     

The electric field effect on binding energy of hydrogenic impurity in zinc-blende GaN/AlxGa1−xN spherical quantum dot

Within the framework of effective mass approximation, the binding energy of a hydrogenic donor impurity in zinc-blende GaN/Al_xGa_1−xN spherical quantum dot (QD) is investigated using the plane wave basis. The results show that the binding energy is highly dependent on impurity position, QD size, Al content and external field. The binding energy is largest when the donor impurity is located at the centre of the QD and the binding energy of impurity is degenerate for symmetrical positions with respect to the centre of QD without the external electric field. The maximum of the donor binding energy is shifted from the centre of QD and the degenerating energy levels for symmetrical positions with respect to the centre of QD are split in the presence of the external electric field. The binding energy is more sensitive to the external electric field for the larger QD and lower Al content. In addition, the Stark shift of the binding energy is also calculated.     

Hydrogenic impurity states in zinc-blende GaN/AlN coupled quantum dots

Based on the effective-mass approximation, we have calculated the donor binding energy of a hydrogenic impurity in zinc-blende (ZB) GaN/AlN coupled quantum dots (QDs) using a variational method. Numerical results show that the donor binding energy is highly dependent on the impurity position and coupled QDs structural parameters. The donor binding energy is largest when the impurity is located at the center of quantum dot. When the impurity is located at the interdot barrier edge, the donor binding energy has a minimum value with increasing the interdot barrier width.     

外电场下极性量子阱中杂质态结合能

我们用变分方法研究了外电场下量子阱中的杂质态结合能,计算中既考虑了电子同体纵光学声子和界面光学声子的相互作用又考虑了杂质中心同体纵光学声子和界面光学声子的相互作用。我们以GaAs/Al_0.3Ga_0.7As量子阱为例,讨论了结合能随杂质位置、阱宽和电场强度的变化规律。得到了电子-声子相互作用对杂质态结合能和斯塔克效应的修正是相当明显的。     

External electric field and hydrostatic pressure effects on the binding energy and self-polarization of an off-center hydrogenic impurity confined in a GaAs/AlGaAs square quantum well wire

Based on the effective-mass approximation within a variational scheme, binding energy and self-polarization of hydrogenic impurity confined in a finite confining potential square quantum well wire, under the action of external electric field and hydrostatic pressure, are investigated. The binding energy and self-polarization are computed as functions of the well width, impurity position, electric field, and hydrostatic pressure. Our results show that the external electric field and hydrostatic pressure as well as the well width and impurity position have a great influence on the binding energy and self-polarization.