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.     

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 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 Binding Energy in GaAs/Ga_(1-x) Al_xAs 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/Ga1-xAlx As 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.     

Finite barrier width effects on exciton states and optical properties in wurtzite InGaN/GaN quantum well

Exciton states and optical properties in wurtzite (WZ) InGaN/GaN quantum well (QW) are investigated theoretically, considering finite barrier width and built-in electric field effects. Numerical results show that when the barrier width increases, the ground-state exciton binding energy, the interband transition energy and the integrated absorption probability increase first and then they are insensitive to the variation of the barrier width. For any barrier width, the ground-state exciton binding energy and the integrated absorption probability have a maximum when the well width is 1 nm; moreover, the integrated absorption probability goes to zero when the well width is larger than 6 nm. In addition, the competition effects between the built-in electric field and quantum confinement are also investigated in the WZ InGaN/GaN QW.     

外电场对直接带隙Ge量子阱中的光学性质的影响

在有效质量近似下,考虑到外电场的影响,详细研究了直接带隙Ge/GeSi量子阱中带间光跃迁吸收系数和阈值能量随量子阱阱宽,外电场强度的变化情况。结果表明：随着外电场的增强,带间光跃迁吸收强度会逐渐减弱,阈值能量减小,吸收曲线向低能方向移动,出现了红移现象。此外,当量子阱比较大时,外电场对量子阱中带间光跃迁阈值能量的影响更加明显。     

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.     

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.     

Electric field effect on the donor impurity states in zinc-blende symmetric InGaN/GaN coupled quantum dots

Based on the effective-mass approximation, the donor binding energy in a cylindrical zinc-blende (ZB) symmetric InGaN/GaN coupled quantum dots (QDs) is investigated variationally in the presence of an applied electric field. Numerical results show that the ground-state donor binding energy is highly dependent on the impurity positions, coupled QDs structure parameters and applied electric field. The applied electric field induces an asymmetric distribution of the donor binding energy with respect to the center of the coupled QDs. When the impurity is located at the center of the right dot, the donor binding energy has a maximum value with increasing the dot height. Moreover, the donor binding energy is the largest and insensitive to the large applied electric field (F?400 kV/cm) when the impurity is located at the center of the right dot in ZB symmetric In_0.1Ga_0.9N/GaN coupled QDs. In addition, if the impurity is located inside the right dot, the donor binding energy is insensitive to large middle barrier width (Lmb?2.5 nm) of ZB symmetric In_0.1Ga_0.9N/GaN coupled QDs.     

The donor bound exciton states in wurtzite GaN quantum dot

Based on the effective mass approximation, the donor bound exciton states in a wurtzite (WZ) GaN/AlGaN quantum dot (QD) are investigated by means of a variational method, including the strong built-in electric field effect due to the spontaneous and piezoelectric polarizations. Numerical results show that the donor bound exciton binding energy is highly dependent on the impurity position and QD size. In particular, we find that the donor bound exciton binding energy is insensitive to dot height when the impurity is located at the right boundary of the WZ GaN/AlGaN QD with large dot height.     

Excitonic optical absorption in wurtzite InGaN/GaN quantum wells

Within the framework of the effective-mass and envelope function theory, exciton states and optical properties in wurtzite (WZ) InGaN/GaN quantum wells (QWs) are investigated theoretically considering the built-in electric field effects. Numerical results show that the built-in electric field, well width and in composition have obvious influences on exciton states and optical properties in WZ InGaN/GaN QWs. The built-in electric field caused by polarizations leads to a remarkable reduction of the ground-state exciton binding energy, the interband transition energy and the integrated absorption probability in WZ InGaN/GaN QWs with any well width and In composition. In particular, the integrated absorption probability is zero in WZ InGaN/GaN QWs with any In composition and well width L > 4 nm. In addition, the competition effects between quantum confinement and the built-in electric field (between quantum size and the built-in electric field) on exciton states and optical properties have also been investigated.     

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.     

Intraband photoresponse of SiGe quantum dot/quantum well multilayers

In this contribution we study the intravalence band photoexcitation of holes from self-assembled Ge quantum dots (QDs) in Si followed by spatial carrier transfer into SiGe quantum well (QW) channels located close to the Ge dot layers. The structures show maximum response in the important wavelength range 3–5 μm. The influence of the SiGe hole channel on photo- and dark current is studied depending on temperature and the spatial separation of QWs and dot layers. Introduction of the SiGe channel in the active region of the structure increases the photoresponsivity by up to about two orders of magnitude to values of 90 mA/W at T=20 K. The highest response values are obtained for structures with small layer separation (10 nm) that enable efficient transfer of photoexcited holes from QD to QW layers. The results indicate that Si/Ge QD structures with lateral photodetection promise very sensitive large area mid-infrared photodetectors with integrated readout microelectronics in Si technology.     

Built-in electric field effect on hydrogenic impurity in wurtzite GaN/AlGaN quantum dot

The binding energy of a hydrogenic donor impurity in a wurtzite (WZ) GaN/AlGaN quantum dot (QD) is investigated, including the strong built-in electric field effect due to the spontaneous and piezoelectric polarizations. Numerical results show that the strong built-in electric field induces an asymmetrical distribution of the donor binding energy with respect to the center of the QD. The donor binding energy is insensitive to dot height when the impurity is located at the right boundary of the QD with large dot height.     

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.     

Laser effects on the donor states in V-shaped and inverse V-shaped quantum wells

Laser effects on the electronic states in GaAs/ Ga_1−xAl_xAs V-shaped and inverse V-shaped quantum wells under a static electric field are studied using the transfer matrix method. The dependence of the donor binding energy on the laser field strength and the density of states associated with the impurity is also calculated. It is demonstrated that in inverse V-shaped quantum wells under electric fields, with an asymmetric distribution of the electron density, the position of the binding energy maximum versus the impurity location in the structure can be adjusted by the intensity of the laser field. This effect could be used to tune the electronic levels in quantum wells operating under electric and laser fields without modifying the physical size of the structures.     

The electric field dependence of a donor impurity in graded <Emphasis Type="Bold">GaAs</Emphasis> quantum wires

The effect of the electric field on the binding energy of the ground state of a shallow donor impurity in a graded GaAs quantum-well wire (GQWW) was investigated. The electric field was applied parallel to the symmetry axes of the wire. Within the effective mass approximation, we calculated the binding energy of the donor impurity by a variational method as a function of the wire dimension, applied electric field, and donor impurity position. We show that changes in the donor binding energy in GQWWs strongly depend not only on the quantum confinement, but also on the direction of the electric field and on the impurity position. We also compared our results with those for the square quantum-well wire (SQWW). The results we obtained describe the behavior of impurities in both square and graded quantum wires. PACS 68.65.-k; 71.55.-i; 71.55.Eq     

Polaron effects on the binding energy of a double donor impurity in quantum wells in an electric field

The binding energy of the single and double bound polaron bound to a helium-type donor impurity in quantum wells (QWs) subject to a perpendicular electric field are calculated by a variational method. The couplings of an electron and the impurity with various phonon modes are considered. The results show that the cumulative effects of the electron–phonon coupling and the impurity–phonon coupling can contribute appreciably to the binding energy for the single bound polaron but only in some severe conditions for the double bound polaron. They also show that the binding energy is sensitive to the electric field strength. The comparison between the binding energies in the case of the impurity placed at the quantum well center and at the quantum well edge is also given.     

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.     

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。