Cylindrical Quantum-well Wires Research Articles

Effect of pressure, temperature, and magnetic field on the binding energy of the electron-hole system in III-V group semiconductors

In this study, ground state binding energy of heavy hole magneto exciton in GaAs/In0.47Ga 0.53As cylindrical quantum well wires (CQWWs) were calculated using variational technique depending on wire size and external parameters. We can briefly state the change of binding energy with hydrostatic pressure, temperature, wire radius and external magnetic field strength as follows. With increasing temperature for constant pressure and magnetic field, the exciton binding energy decreases slightly. On the other hand, increasing magnetic field strength and pressure increase the binding energy as the particle's quantum confinement effects increase. To interpret these results, we examined pressure and temperature changes of barrier heights, effective masses, wire radius, dielectric constant, and band offsets. Conduction and valence band offset increase by 37% with pressure, while band offsets decrease by -1.55% with temperature. These differences in values are directly due to the difference in pressure and temperature coefficients of the prohibited band gaps of GalnAs and InAs. These variations in binding energy, as well as in electron and hole energies, depending on structure parameters and external parameters provide a prediction to produce adjustable semiconductor devices.

Pressure and temperature effects on magnetoelectric band energies in GaAs / InxGa1-xAs cylindrical quantum wires

Low-dimensional systems, consisting of GaAs / InGaAs heterostructures, have attracted considerable attention due to their many applications in optoelectronic and microelectronic devices. In the present work, the electron and the heavy-hole ground state energy in an InGaAs/GaAs cylindrical quantum well wires (CQWWs) is investigated with the consideration of geometrical confinement. The ground state energy was calculated as a function of hydrostatic pressure and temperature. Under the constant pressure and at a certain magnetic field value, while the ground state energy of the electron and the hole decreases depending on the temperature, it is observed that the energy increases as the hydrostatic pressure increases under the constant temperature. These calculations are interpreted with graphics.

The hydrostatic pressure and temperature effects on the binding energy of magnetoexcitons in cylindrical quantum well wires

We have calculated the binding energy for the ground state of a heavy-hole exciton in GaAs/Ga0.7Al0.3As cylindrical quantum well wires (CQWWs) under the action of a hydrostatic pressure, temperature and magnetic field. The calculations are made using variational methods and the effective mass approximation for a finite confinement potential. The hydrostatic pressure, temperature and magnetic field effects can be summarized as follows; excitonic binding energy is a decreasing function of temperature for fixed pressure and magnetic field also is an increasing function of pressure for fixed temperature and magnetic field values depending on the applied pressure range. For larger magnetic field strengths, the binding energies get larger for any hydrostatic pressure and temperature values as expected.

Hydrogenic impurity states in zinc-blende In xGa 1− xN/GaN in cylindrical quantum well wires under hydrostatic pressure

Within the framework of effective-mass approximation, the binding energy of a hydrogenic donor impurity in zinc-blende (ZB) In x Ga 1− x N/GaN cylindrical quantum well wires (CQWWs) is investigated using variational procedures. Numerical results show that the ground-state donor binding energy E b increases when the hydrostatic pressure increases for any impurity position. The donor binding energy for a shallow donor impurity located at the center of the CQWWs is the largest. Also, we have found that In concentration is very important value to tailor the system, since the binding energies close to binding energy maxima are strongly dependent to In content.

Hydrogenic impurity states in zinc-blende In xGa 1−xN/GaN in cylindrical quantum well wires

Within the framework of effective-mass approximation, the binding energy of a hydrogenic donor impurity in zinc-blende (ZB) In x Ga 1 − x N/GaN cylindrical quantum well wires (CQWWs) is investigated using variational procedures. Numerical results show that the ground-state donor binding energy E b is highly dependent on the impurity position and the CQWWs structure parameters. The donor binding energy for a shallow donor impurity located at the center of the CQWWs is the largest. As the impurity position changes from the center of the wire to its edge, the donor binding energy gets smaller. Also, we have found that In concentration is a very important value to tailor the system, since the binding energies close to binding energy maxima are strongly dependent on In content.

The effects of pressure and barrier height on donor binding energy in GaAs/Ga 1− xAl xAs cylindrical quantum well wires

The ground state binding energy of axial hydrogenic impurity in GaAs/Ga 1− x Al x As cylindrical quantum well wires (CQWWs) are investigated as a function of the barrier height and the radius of the wire under hydrostatic pressure in the effective mass approximation and variational calculation scheme. The effect of applied hydrostatic pressure is introduced into the calculations using pressure dependent values of energy gap, effective mass and dielectric constant. We have found that for large radii the binding energies are not affected by applied pressure. However, in the region where the particles interact with the barrier the binding energy is strongly dependent on the hydrostatic pressure for all x values. Furthermore, we have shown that this dependency is as strong as the binding energy increase via Al concentration increase.

Laser-dressing and magnetic-field effects on shallow-donor impurity states in semiconductor GaAs–Ga1−xAlxAs cylindrical quantum-well wires

The influence of an intense laser field on shallow-donor states in cylindrical GaAs–Ga1−xAlxAs quantum-well wires under an external magnetic field applied along the wire axis is theoreticallystudied. Numerical calculations are performed in the framework of the effective-massapproximation, and the impurity energies corresponding to the ground state and2p ± excited states are obtained via a variational procedure. The laser-fieldeffects on the shallow-donor states are considered within the extendeddressed-atom approach, which allows one to treat the problem ‘impurity+ heterostructure+ laser field+ magnetic field’ as arenormalized ‘impurity + heterostructure + magnetic field’ problem, in which the laser effects are taken into account through arenormalization of both the conduction-band effective mass and fundamentalsemiconductor gap.

Electron–phonon interaction effect on optical absorption in cylindrical quantum wires

Electron–phonon interaction effects on linear and nonlinear optical absorption in cylindrical quantum wires are investigated. The linear and nonlinear optical absorption coefficients are obtained by using compact-density-matrix approach and iterative method, and the numerical results are presented for GaAs/AlAs cylindrical quantum-well wires. The results show that electron–phonon interaction not only influences the relaxation rate but also distinctly influences the wave functions and energies of the electron. The correction of electron–phonon interaction effect on the wave functions of the electron dominates the values of absorption coefficients. Moreover, the correction of electron–phonon interaction effect on the energies of the electron makes the absorption peaks blue shift and become wider.

Correlated electron–hole transition energies in quantum-well wires: Effects of hydrostatic pressure

We perform a theoretical study, using a variational approach, of the effects of hydrostatic pressure on the exciton binding energies and photoluminescence peak positions in GaAs – Ga 1 - x Al x As cylindrical quantum-well wires within the effective-mass approximation. Calculated results suggest that future device applications may be realized by properly varying the wire dimensions and applying hydrostatic pressure.

Interface and surface optical phonons in a free-standing [formula omitted] cylindrical quantum-well wire

Under dielectric continuum approximation, interface optical (IO) and surface optical (SO) phonon modes as well as the corresponding Fröhlich electron–phonon interaction Hamiltonian in a free-standing cylindrical quantum-well wire (QWW) were derived and studied. Numerical calculations on GaAs / Al x Ga 1 - x As cylindrical QWWs have been performed. Results reveal that, in the case of taking the “two-mode” behavior of the Al x Ga 1 - x As material into account, there have four branches of IO phonon modes and two branches of SO phonon mode, and the dispersion frequencies of IO or SO phonon modes sensitively depend on the Al mole fraction x in Al x Ga 1 - x As material and the wave-vector in z direction k z . With the increasing of k z and quantum number m, the frequency of each IO mode approaches one of the two frequency values of the single GaAs / Al x Ga 1 - x As heterostructure, and the electrostatic potential distribution of the phonon mode tends to be more and more localized at a certain interface or surface, meanwhile, the coupling between the electron-IO or -SO phonon becomes weaker.

Laser effects on donor states in low-dimensional semiconductor heterostructures

A theoretical study of the effects of intense laser fields on the ground-state binding energies of donor impurities in low-dimensional semiconductor heterostructures is performed. The laser-heterostructure interaction is treated within an extended dressed-atom approach, so that, for a laser tuned far below any resonances, the effects of the laser-semiconductor interaction correspond to a renormalization of the semiconductor energy gap and conduction/valence effective masses. Calculations are performed for donors in $\mathrm{GaAs}\text{\ensuremath{-}}(\mathrm{Ga},\mathrm{Al})\mathrm{As}$ quantum wells, cylindrical quantum-well wires, and spherical quantum dots. The binding energies of donors in low-dimensional systems increase with increasing laser intensity, and for a fixed intensity, the influence of the laser is stronger for small detunings. Results obtained within the extended dressed-atom approach are compared with previous calculations performed by using a simplified high-frequency limit of the Kramers-Henneberger approach.

Polaron effects on third-harmonic generation in cylindrical quantum-well wires

Polaron effects on third-harmonic generation (THG) in cylindrical quantum wires with a finite confining potential are investigated. The THG coefficient is obtained by using the compact-density-matrix approach and an iterative method, and the numerical results are presented for GaAs/AlAs cylindrical quantum wires. The results show that the THG coefficient is greatly enhanced and the peak shift to the aspect of high energy when considering the influence of electron–phonon interaction.

Polar Oscillation of Interface and Surface Optical Phonons in Free-Standing Cylindrical Quantum-Well Wires**The project supported partly by Natural Science Foundation of Guangdong Province of China

Under dielectric continuum approximation, interface optical (IO) and surface optical (SO) phonon modes as well as the corresponding Fröhlich electron-phonon interaction Hamiltonian in a free-standing cylindrical quantum-well wire (QWW) are derived and studied. Numerical calculations on As cylindrical QWW are performed. Results reveal that there are two branches of IO phonon modes and one branch of SO phonon mode, and the dispersion frequencies of IO or SO phonon modes sensitively depend on the Al mole fraction in As material and the wave-vector in direction, . With the increasing of and quantum number , the frequency of each IO mode approaches one of the two frequency values of the single As heterostructure, and the electrostatic potential distribution of the phonon mode tends to be more and more localized at a certain interface or surface, meanwhile, the coupling between the electron-IO and -SO phonons becomes weaker.

TRANSFER MATRIX METHOD FOR THE FRÖHLICH ELECTRON–INTERFACE OPTICAL PHONON INTERACTION IN MULTILAYER COAXIAL CYLINDRICAL QUANTUM-WELL WIRES

Under dielectric continuum approximation, by adopting the transfer matrix method, interface optical (IO) phonon modes and the Fröhlich electron–IO-phonon interaction Hamiltonian in a multilayer coaxial cylindrical quantum-well wire (QWW) were deduced and investigated. Numerical calculations on a four-layer GaAs / Al x Ga 1-x As QWW have been performed. Results reveal that there are six branches of IO phonon modes. When the wave vector in z-direction kz and the azimuthal quantum number m are small, the dispersion frequencies of IO modes sensitively depend on kz and m. When kz and m are relatively large, with the increasing of kz and m, the frequency for each mode converges the limit frequency value of IO mode in single heterostructure, and the electrostatic potential distribution of each mode tends to be more and more localized at the interfaces, meanwhile, the coupling between the electron–IO-phonon becomes weaker and weaker. The calculation also shows that the phonon modes with higher frequencies have more significant contribution to the electron–phonon interaction. At last, it is found that kz and m have analogous effects on the frequencies and the electrostatic potentials of the IO phonons.

Density of electronic states in impurity-doped quantum well wires

We analyze the electronic states in the cylindrical quantum well-wire (QWW) with randomly distributed neutral, D 0 and negatively charged D − donors. In order to calculate the ground state energies of the off-center donors D 0 and D − as a function of the distance from the axis of QWW we use the recently developed fractal dimension method in which the problems are reduced to a similar one for a hydrogen-like atom and a negative-hydrogen-like ion respectively, in an isotropic effective space with variable fractional dimension. The numerical trigonometric sweep method and the three-parameter Hylleraas trial function are used to solve these problems. We present a novel curves for the density of impurity states in a cylindrical QWWs with square-well, parabolic and soft-edge barrier potentials. Additionally we analyze the effect of the repulsive core on the density of the impurity states.

Shallow-donor states in semiconductor heterostructures within the fractional-dimensional space approach

Shallow-donor states in quantum-sized semiconductor heterostructures are studied within the fractional-dimensional space approach. Calculations were performed for the binding energies of the ground state of donors in GaAs–(Ga,Al)As quantum wells, cylindrical quantum-well wires, and spherical quantum dots. Fractional-dimensional theoretical results are shown to be in good agreement with previous variational calculations.

Optical and acoustic plasmons in cylindrical quantum-well wires.

We study theoretically the collective electronic excitations of quasi-one-dimensional cylindrical quantum-well wires, the intrasubband and intersubband plasmons in the random-phase approximation. Using a two-subband model we calculate the dispersion curves for the case that two subbands are occupied. We study the influence of the image forces on the intrasubband and intersubband plasmons in detail. These modes are split in two branches. The intrasubband plasmon branches can be classified in an optical and an acoustic branch which are influenced quite differently by the image forces. The intersubband plasmon branches behave like acoustic plasmons.

A perturbation-variational treatment of hydrogenic impurity states in quantum wires

The binding energy of a hydrogenic impurity placed on the axis of a cylindrical quantum-well wire is studied using a perturbation-variational expansion method to the first order in the perturbation expansion. The variations of the binding energy with the radius and barrier height of the quantum-well wire are obtained. When the radius of the wire becomes very large or the barrier height of the quantum-well is very small, the impurity behaves like a free hydrogenic atom with a ground-state energy of one effective Rydberg.

Photoluminescence study of shallow acceptors in GaAs-Ga1-xAlxAs cylindrical quantum-well wires.

A systematic study of the theoretical acceptor-related photoluminescence spectra in a cylindrical GaAs-(Ga,Al)As quantum-well wire is performed. The acceptor states are described within a variational scheme in the effective-mass approximation. Photoluminescence spectra associated with acceptors are calculated for both homogeneous and on-center spike-doped distributions of acceptors in the quantum-well wire. Results are dependent on the temperature, on the choice of the quasi-Fermi-energy level of the conduction-subband electron gas, and on the distribution of acceptors in the wire. The photoluminescence spectra corresponding to the on-center spike-doped Gaussian distribution (width of the doping spike of the order of 50 \AA{}) shows a peak for energies associated with on-center impurity states, as is expected, whereas for a homogeneous distribution of acceptors in the well we essentially found an edge in the spectra associated with transitions involving on-center acceptors and a peaked structure related to the onset of transitions from the conduction subband to on-edge acceptors. Although no experimental results for GaAs-(Ga,Al)As quantum-well wires are available, our results agree qualitatively with previous theoretical and experimental work on GaAs-(Ga,Al)As quantum-well heterostructures.

Hydrogenic impurity in quantum-well wires/effects of the image charges

The ground state binding energy of a hydrogenic impurity placed on the axis of a cylindrical quantum-well wire is calculated including the effects of the image charges and the finite barrier. A variational anzatz for the wave function of the electron, that takes into account the three-dimensional behavior of the electron in small wires, has been used. Numerical results for GaAs-Ga 1- x Al x As quantum-well wires show that the effects of the image charges cause a considerable enhancement of the ground state binding energy of the impurity, especially in the case of high values of the Al composition and small wires.