Shallow Donor Impurity States Research Articles

Shallow-donor impurity states in type-II InGaN-ZnSnN2/GaN quantum wells under hydrostatic pressure effect

Shallow-donor impurity states in type-II InGaN-ZnSnN2/GaN quantum wells under hydrostatic pressure effect

Shallow Donor Impurity States with Excitonic Contribution in GaAs/AlGaAs and CdTe/CdSe Truncated Conical Quantum Dots under Applied Magnetic Field.

Using the effective mass approximation in a parabolic two-band model, we studied the effects of the geometrical parameters, on the electron and hole states, in two truncated conical quantum dots: (i) GaAs-(Ga,Al)As in the presence of a shallow donor impurity and under an applied magnetic field and (ii) CdSe–CdTe core–shell type-II quantum dot. For the first system, the impurity position and the applied magnetic field direction were chosen to preserve the system’s azimuthal symmetry. The finite element method obtains the solution of the Schrödinger equations for electron or hole with or without impurity with an adaptive discretization of a triangular mesh. The interaction of the electron and hole states is calculated in a first-order perturbative approximation. This study shows that the magnetic field and donor impurities are relevant factors in the optoelectronic properties of conical quantum dots. Additionally, for the CdSe–CdTe quantum dot, where, again, the axial symmetry is preserved, a switch between direct and indirect exciton is possible to be controlled through geometry.

The anisotropy effects on the shallow-donor impurity states and optical transitions in quantum dots

The anisotropy effects on the shallow-donor impurity states and optical transitions in quantum dots

Binding energy and optical absorption of donor impurity states in “12-6” tuned GaAs/GaAlAs double quantum well under the external fields

We have investigated the binding energies of the s-symmetric ground and first excited shallow donor impurity states and the total 1s → 2s absorption coefficient, including the first and third order corrections, in “12-6” tuned GaAs/GaAlAs double quantum well as a function of the impurity position, size of the structure, and the electric and magnetic field intensities. The obtained results show that the electronic and optical properties of tuned GaAs/GaAlAs double quantum well can be adjustable by an appropriate choice of the sample geometry, material parameters and applied external fields which will lead to new potential applications in optoelectronics.

Impurity states in InSe monolayers doped with group II and IV elements

We have used first-principles calculations to investigate the electronic structures of two-dimensional (2D) InSe monolayers doped with group II and IV elements. The results show that substituting Mg, Ca, Ge, and Sn for indium clearly modifies the electronic and magnetic properties of InSe monolayers and that these substitutions should be easily achieved in a Se-rich environment. Mg- and Ca-doped InSe monolayers develop deep acceptor states and magnetism, whereas substituting Ge and Sn for In induces shallow donor impurity states in these monolayers. Furthermore, the results show that substituting Sn for In provides effective n-type carriers in the InSe monolayer because of the low formation energy and transition level (∼61.10 meV). These results should be helpful for related experimental studies.

Combined effects of an intense laser field, electric field and hydrostatic pressure on donor impurity states in zinc-blende InGaN/GaN quantum dots

The shallow-donor impurity states in cylindrical zinc-blende (ZB) InxGa1−xN/GaN quantum dots (QDs) have been theoretically investigated, considering the combined effects of an intense laser field (ILF), an external electric field, and hydrostatic pressure. The numerical results show that for an on-center impurity in ZB InxGa1−xN/GaN QD, (1) the ground-state binding energy of the donor impurity is a decreasing function of the laser-dressing parameter and/or the QD’s height; (2) as the QD’s radius decreases, the binding energy of the donor impurity increases at first, reaches a maximum value, and then drops rapidly; (3) the binding energy of the donor impurity is a decreasing function of the external electric field due to the Stark effect; (4) the binding energy of the donor impurity increases as the applied hydrostatic pressure becomes large. In addition, the position of the impurity ion was also found to have an important influence on the binding energy of the donor impurity. The physical reasons have been analyzed in detail.

Intense Laser Field Effects on the Shallow-Donor Impurity States in Rectangular-Shaped Quantum Well Wires

3rd International Congress on Advances in Applied Physics and Materials Science -- APR 24-28, 2013 -- Antalya, TURKEY

Shallow-donor impurity in vertical-stacked InGaN/GaN multiple-quantum wells: Electric field effect

Based on the effective-mass approximation, the electric field effect on the shallow-donor impurity states in vertical-stacked zinc-blende (ZB) InGaN/GaN multiple-quantum wells (MQWs) is investigated variationally. Numerical results show that if the electric field applied to the right (along the growth direction), the donor binding energy has a maximum value and the position of the maximum value is located inside the left well. Moreover, in the presence of the electric field, the donor binding energy of impurity located at the center of the left well is insensitive to the increment of the barrier width when the barrier width is large. In particular, it is also found that the donor binding energy of impurity located at the center of the left well in the MQWs has a maximum value with the increase in electric field and the critical electric field of the maximum value is reduced when the well width is increased.

Shallow-donor impurity in zinc-blende InGaN/GaN asymmetric coupled quantum dots: Effect of electric field

We have performed a theoretical calculation of the shallow-donor impurity states in cylindrical zinc-blende (ZB) InGaN/GaN asymmetric coupled quantum dots (QDs), considering the effect of the electric field applied to the left (opposite to the growth direction). Numerical results show that the donor binding energy in ZB InGaN/GaN asymmetric coupled QDs is highly dependent on the impurity positions, asymmetric coupled QD structure parameters, and the electric field. In the presence of the electric field, if the left dot height is increased from zero, the donor binding energy of the impurity localized inside the middle barrier layer has a maximum value; if the right dot is increased from zero, the donor binding energy of impurity localized inside the right dot has a maximum value. It is also found that for the impurity located at the center of the right dot, the donor binding energy is insensible to the electric field when the electric field is large; however, the critical electric field is smaller if the right dot is wide. In particular, numerical results show that if the right dot is wide, the asymmetric coupled QDs are much easier to be decoupled under the influence of the electric field.

MBE growth and transport properties of silicon δ-doped GaAs/AlAs quantum well structures for terahertz frequency detection

We present the electrical characterization of n-type GaAs/AlAs multiple quantum well (MQW) structures designed for terahertz (THz) radiation sensing at cryogenic temperatures. The samples were grown by solid source molecular beam epitaxy (MBE) and were δ-doped with silicon atoms at each potential well center. Temperature dependent Hall effect data show that (i) the conduction in these planar doped structures is thermally activated below 180 K, (ii) the free carriers sheet densities are near the metal–insulator transition, and (iii) the low temperature mobility is controlled by ionized impurities scattering. The study of the magneto-transport properties at 1.3 K further indicates that only the fundamental electronic sub-band of the two-dimensional electronic gas is populated. The MQW samples were then processed into lateral mesa-shaped photodetectors to investigate their spectral response in the THz frequency range. The preliminary experimental results for the proposed detection scheme, which involves transitions in the confined shallow donor impurity states, are described.

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.

Hydrogenic donor impurity in parallel-triangular quantum wires: Hydrostatic pressure and applied electric field effects

The combined effects of the hydrostatic pressure and in-growth direction applied electric field on the binding energy of hydrogenic shallow-donor impurity states in parallel-coupled-GaAs-Ga1-xAlxAs-quantum-well wires are calculated using a variational procedure within the effective-mass and parabolic-band approximations. Results are obtained for several dimensions of the structure, shallow-donor impurity positions, hydrostatic pressure, and applied electric field. Our results suggest that external inputs such us hydrostatic pressure and in-growth direction electric field are two useful tools in order to modify the binding energy of a donor impurity in parallel-coupled-quantum-well wires.

Electronic States of a Shallow Hydrogenic Donor Impurity in Different Shaped Semiconductor Quantum Wells

The shallow hydrogenic donor impurity states in square, V-shaped, and parabolic quantum wells are studied in the framework of effective-mass envelope-function theory using the plane wave basis. The first four impurity energy levels and binding energy of the ground state are more easily calculated than with the variation method. The calculation results indicate that impurity energy levels decrease with the increase of the well width and decrease quickly when the well width is small. The binding energy of the ground state increases until it reaches a maximum value, and then decreases as the well width increases. The results are meaningful and can be widely applied in the design of various optoelectronic devices.

Hydrostatic pressure, electric and magnetic field effects on shallow donor impurity states and photoionization cross section in cylindrical GaAs–Ga1–xAlx As quantum dots

AbstractUsing the variational method and the effective mass approximation, we have calculated the influence of applied electric and magnetic fields, both in the axial direction, and hydrostatic pressure on the binding energy and photoionization cross section for on center shallow‐donor impurities in cylindrical shaped GaAs–Ga1–x Alx As quantum dots. For the hydrostatic pressure effects the Γ–X crossover has been taken into account. Different values for the structure dimensions, applied electric and magnetic fields, hydrostatic pressure, and energy of the incident photon have been considered. Because the parallel polarization of the incident radiation has been considered, the main effects on the photoionization cross section are associated with the applied electric field. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Stress effects on the binding energy of shallow-donor impurities in symmetricalGaAs/AlGaAs double quantum-well wires

The effects of applied compressive stress on the binding energies of shallow-donorimpurity states with a finite confinement potential in symmetrical GaAs/AlGaAsdouble quantum-well wires (DQWWs) are studied theoretically using a variationalprocedure within the effective-mass approximation. Significant results for different wireand barrier widths, shallow-donor impurity positions, and compressive stressalong the growth direction of the structure are obtained taking into account theΓ–X crossover and the image charge effects in the calculations. Our results show that thebinding energy does not change appreciably with the size of the wire and barrier, or withthe donor ion position. We also find that for stress values up to 13.5 kbar, the bindingenergy increases linearly with stress, while for stress values greater than 13.5 kbar, thebinding energies show nonlinear behavior. Moreover, in the limit of double quantumwells (DQWs), our binding energy agrees with previously reported results. It ispointed out that compressive stress is an important factor in studies of the bindingenergies of shallow-donor impurity states in symmetrical GaAs/AlGaAs DQWWs.

The influence of compressive stress on shallow-donor impurity states in symmetric GaAs-Ga1−xAlxAs double quantum dots

The effects of compressive stress on the binding energy of shallow-donor impurity states in symmetrical GaAs-Ga1−xAlxAs double quantum dots are calculated variationally using a parameterized wave function within the effective-mass approximation. Results are obtained for different dot and barrier widths, donor ion positions, and compressive stresses along the growth direction of the structure. In the direct-gap regime (for stress values up to 13.5 kbar) the binding energy increases linearly with the stress. In the indirect-gap regime (for stress values greater than 13.5 kbar) and with the donor ion at the center of the dot, the binding energy increases up to a maximum and then decreases. For all donor ion positions, the binding energy shows nonlinear behavior in the indirect-gap regime due to the Γ-X crossing effect. In the limit of single quantum wells, the results we obtain are in good agreement with those previously obtained for the case in which the donor ion is at the center of the well.

Hydrostatic pressure and electric-field effects on the shallow donor impurity states in GaAs-Ga0.7Al0.3As quantum-well wires

Using a variational procedure within the effective-mass approximation, we have made a theoretical study of the effects of hydrostatic pressure and applied electric fields on the binding energy of a shallow-donor impurity in square-transversal section GaAs-Ga0.7Al0.3As quantum-well wires. The electric field is applied in a plane of the transversal section of the wire and many angular directions are considered. The hydrostatic pressure has been considered both in the direct and indirect gap regime for the Ga0.7Al0.3As material. For the potential barrier that defines the wire region, we consider an x-dependent finite and y-dependent infinite model. The results we present are for the impurity binding energy and considering different values of the wire dimensions, hydrostatic pressure, applied electric field, and the impurity position in the transversal section of the wire.

Stress effects on shallow-donor impurity states in symmetricalGaAs/AlxGa1−xAsdouble quantum wells

The effects of the compressive stress on the binding energy and the density of shallow-donor impurity states in symmetrical ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ double quantum wells are calculated using a variational procedure within the effective-mass approximation. Results are for different well and barrier widths, shallow-donor impurity position, and compressive stress along the growth direction of the structure. We have found that independently of the well and barrier widths, for stress values up to 13.5 kbar (in the direct-gap regime) the binding energy increases linearly with the stress. For stress values greater than 13.5 kbar (indirect gap regime) and for impurities at the center of the wells, the binding energy increases up to a maximum and then decreases. For all impurity positions the binding energy shows a nonlinear behavior in the indirect gap regime due to the $\ensuremath{\Gamma}\ensuremath{-}X$ crossing effect. The density of impurity states is calculated for a homogeneous distribution of donor impurities within the barriers and the wells of the low-dimensional heterostructures. We have found that there are three special structures in the density of impurity states: one associated with on-center-barrier-, the second one associated with on-center-well-, and the third one corresponding to on-external-edge-well-impurity positions. The three structures in the density of impurity states must be observed in valence--to--donor-related absorption and conduction--to--donor-related photoluminescence spectra, and consequently these peaks can be tuned at specific energies and convert the system in a stress detector.

Binding energy and density of shallow impurity states in GaAs–(Ga, Al)As quantum wells: effects of an applied hydrostatic stress

The effects of hydrostatic stress on the binding energy and the density of shallow-donor and shallow-acceptor impurity states in a GaAs–(Ga, Al)As quantum well are calculated using a variational procedure within the effective-mass approximation. Results are for different well widths and hydrostatic stresses, as a function of the impurity position along the growth direction of the structure. We have found that in the low-pressure regime the binding energy changes linearly for both donor and acceptor impurities, independently of the sizes of the well. However, for high pressures (greater than 13.5 kbar) this is valid for acceptors but not for donors due to the Γ-X crossover. We have shown that there are two special structures in the density of impurity states, one associated with on-centre and the other with on-edge impurities. Also, we have observed that the density of impurity states depends strongly on the applied hydrostatic stress.

Intra-donor transitions in triple quantum-well structures under external fields

A theoretical study on shallow donor-impurity states in distinct triple GaAs–(Ga, Al)As quantum-well heterostructures is presented under external magnetic and electric fields applied perpendicular to the interfaces of the semiconducting elements. The emphasis is put on the determination of intra-donor absorption spectra and its dependence on the impurity profile distributions and different photon polarizations are considered. Impurity states are calculated by adopting the effective mass approximation and using a variational scheme in which ground and excited states are obtained simultaneously. Magnetospectroscopy measurements may be used to observe such transitions.