Donor Binding Energy Research Articles

Examining the influence of electric field on the photoionization cross section and spin polaronic shift in a semimagnetic double quantum well

In the current research, we performed a numerical investigation of a shallow donor impurity confined in a diluted magnetic semiconductor (DMS) double quantum well (DQW) made of a Cd1−xwMnxwTe/Cd1−xbMnxbTe under the applied electric field in the z-direction. The optoelectronic properties were carried out using the effective-mass approximation and the variational method. The binding energy and photoionization cross section were examined by considering different factors such as, well width, barrier width, impurity position, and Manganese mole fraction. Additionally, the spin polaronic shift corrections to the donor binding energy, caused by the strong exchange interaction between the magnetic moment of the Mn2+ the confined carrier spin, have been examined under the aforementioned effects.

Hydrogen-like impurities in Si and Ge quantum dots in connection with 5 nm and beyond metal-oxide-semiconductor technologies

The industrial drive towards smaller semiconductor devices is at less than 10 nano-meters. In the next few years a three-dimensional quantum confined device structure is expected. We have studied the electronic structure of hydrogen-like donor impurities in Si and Ge quantum dots with varied shape of the confinement potential. These calculations are carried out within the Density-Functional-Effective-Mass Theory (DF-EMT). We have paid particular attention to the electron-electron interaction energy in a negative charge state of the donor impurity. The effect of electron correlation on the binding energy has been explored. In addition to these, we show that the second order correction to the ground state energy obtained through perturbative approach agrees well with the DF-EMT based numerical results, down to very small sizes of the quantum dots when the depth of the confinement is moderate or small. A non-monotonic shallow-deep transition of the binding energy of neutral and charged donors of hydrogen-like impurities is expected to occur with the reduction in the size of the quantum dot. A similar effect is expected for hydrogen-like acceptor impurities as well. Furthermore, the optical gap also shows non-monotonic shallow-deep behaviour with the quantum dot size reduction. Deepening of shallow donor or acceptor level implies that the carriers will freeze out at small sizes of the dot. We believe this is quite important in the context of metal-oxide-semiconductor (MOS) devices beyond 5 nm technologies, based on Si, Ge or a combination (SiGe). We also point out possible variabilities in the binding energy of donors and acceptors if there are variations in the size of host quantum dots in a large assembly of devices in future integrated circuits. This will lead to the variabilities in the characteristics from device to device. These results should be incorporated in the Technology Computer Aided Design (TCAD) simulation of less than or equal to 5 nm MOS devices.

Electron binding energy of donors in bilayer graphene with a gate-tunable gap

Electron binding energy of donors in bilayer graphene with a gate-tunable gap

Examining the influence of magnetic field on a donor dopant’s photoionization cross-section in a double quantum box

This study systematically explored the binding energy and the photoionization cross-section (PCS) of a hydrogenic shallow donor impurity within a GaAs double quantum box structure incorporated into a Ga(1−x)Alx As matrix under the influence of an external intense magnetic field. The computations are performed using the effective-mass approximation (EMA) and the finite element method (FEM), taking into account a finite potential across all surfaces of the nanosystem. The results emphasize the significant role of the magnetic field, primarily in enhancing the donor binding energy within the double quantum box system. We demonstrate that increasing the magnetic field results in an augmentation of binding energy across various aluminum concentrations. The PCS of a shallow donor impurity undergoes a blue shift when shifted from the barrier center to the box center, attributed to the increased binding energy. When the double quantum box is subjected to a magnetic field effect, the amplitude peaks of PCS show an elevation coupled with a blue shift. By setting magnetic field values at 0 T, 35 T, or 70 T and varying aluminum concentrations, we observe a shift in the PCS towards higher energy levels along with an increase in peak amplitude. We also study the PCS of the donor impurity as a function of photon energy, mainly examining the effects of box width and barrier width modifications in the double quantum box.

Binding energies of shallow donors in polar ZnO/ZnBeO quantum well

This study examines a single wurtzite ZnO/ZnBeO quantum well structure oriented in the polar c-direction. The focus is on investigating the binding energies associated with an impurity donor atom within this system. To achieve this, a self-consistent solution to the Schrödinger and Poisson equations is obtained using the finite difference method. The framework employed involves the effective mass and envelope function approximations. The impurity is represented using a hydrogenic-type wave function, and donor binding energies are determined via a variational approach. The research analyzes the binding energies of the 1s and 2p± states, along with the transition energy between them. These quantities are explored as functions of the well width and Be concentration, considering donor positions at the right and left interfaces as well as at the well’s center. Furthermore, the impact of an external magnetic field oriented along the growth direction is assessed, spanning up to 10T, in order to quantify changes in the binding energies. The presence of a built-in electric field induces an asymmetric band profile and a triangular well configuration. This asymmetry results in a loss of symmetry within the binding energy curves. Ultimately, the investigation culminates in the computation of the oscillator strength governing transitions between the donor states. When the donor is situated at the right interface, the energy values remain relatively constant as the well width increases, and the oscillator strength values demonstrate a consistent linear rise.

On the semiconductor to metal transition in a quantum wire: Influence of geometry and laser

The diamagnetic susceptibility and binding energy (BE) of a hydrogenic donor confined in a GaAs/AlGaAs QWW were theoretically studied in this paper under the influences of the applied laser field, QWW geometry, and non-parabolicity using variation technique combined with effective mass approximation. In the first part, the diamagnetic susceptibility and BE of the donor at the ground state are studied as a function of the size of the QWW, geometry, and applied laser field. The results reveal that changing the geometry of QWW enhances the quantum confinement effects. However, increasing the laser field reduces the BE by adding screening effects to the Coulomb interactions. Further, the diamagnetic susceptibility is available with the stability information about the carrier–parent donor system based on the mean square separation between them. It also demonstrates that susceptibility may remain stable regardless of the change in geometry and applied laser field. Thus, the diamagnetic behavior can serve as a better tool to evaluate the stability and Mott transition of donors in QWW. In the second section, the consequences of laser field and geometry on the SMT of confined donors in QWW have been studied. It is observed that the BE of donors remains constant until [Formula: see text] cm[Formula: see text] beyond which it starts to decrease gradually and vanishes exactly at critical concentration ([Formula: see text]. However, the diamagnetic susceptibility of the donor has remained constant until reaching [Formula: see text], beyond which it turned into a drastic fall, which manifested the SMT in the system. The current work is expected to add a few noteworthy points to the SMT phenomena in nanostructures.

Hydrostatic pressure, electric field, non-parabolicity and polaronic mass effects on the donor binding energy in a semimagnetic double quantum well

Hydrostatic pressure, electric field, non-parabolicity and polaronic mass effects on the donor binding energy in a semimagnetic double quantum well

Effect of tilted magnetic field on the binding energy of a hydrogenic donor in a near triangular quantum well

ABSTRACT Low-dimensional semiconductor systems have attracted considerable attention of the researchers because of their applications such as speed circuits, optical devices etc. The application of external perturbations like magnetic field can change the properties of these systems. Study on tilted magnetic fields is of interest theoretically as it illustrates special confinement effects. In the present study, we calculate the binding energy of a hydrogenic donor in a quantum well with a potential profile proportional to |z|2/3, called Near Triangular Quantum Well (NTQW), in the presence of a magnetic field tilted by an angle θ with the growth axis, using variational method. Calculations of hydrogenic donor binding energies are made by varying the well width (L), Aluminium composition (x), strength of the magnetic field (γ) and the tilt angle (θ). Integrated probability density (P) of finding a hydrogenic donor in NTQW is also analysed as a function of well width (L).

Photo-ionisation cross-section of a hydrogenic donor in a near triangular quantum well

ABSTRACT Ground state and first excited state binding energies of a hydrogenic donor in a near triangular quantum Well (NTQW) composed of GaAs/Ga1-xAlxAs are calculated variationally as a function of well width and Al concentration. Photo-ionisation cross-section of the donor is also investigated as a function of photon energy, well width and Al concentration. Our results reveal that the peak value of photo-ionisation cross-section shows a turnover at the well width at which the binding energy is a maximum and at the Al concentration of 0.3. Photo-ionisation shows a strong dependence on well width, Al concentration and photon energy in NTQW than in other nanostructures.

Quasiparticle self-consistent GW band structures and phase transitions of LiAlO2 in tetrahedrally and octahedrally coordinated structures

A first-principles computational study is presented of various phases of LiAlO$_2$.The $\beta$ and $\gamma$ tetrahedral phases are found to be very close in energy with the $\gamma$ phase having the lowest energy. The octahedral $\alpha$ phase is a high-pressure phase and the transition pressure from the $\gamma$ and $\beta$ phases to $\alpha$ is determined to be about 1 GPa. The electronic band structures are determined using the quasiparticle self-consistent (QS) $GW$ method. The effective masses of the band edges and the nature of the band gaps are presented. The lowest energy $\gamma$ phase is found to have a pseudodirect gap of 7.69 eV. The gap is direct at $\Gamma$ but corresponds to a dipole forbidden transition. The imaginary part of the dielectric function and the absorption coefficient are calculated in the long-wavelength limit and the random phase approximation, without local field or electron-hole interaction effects for each phase and their anisotropies are discussed. Si doping on the Al site is investigated as a possible $n$-type dopant in $\gamma$-LiAlO$_2$ using a 128 atom supercell corresponding to 3.125 \% Si on the Al sublattice in the generalized gradient approximation and a smaller 16 atom cell with 25 \% Si in the QS$GW$ approximation. The Si is found to significantly perturb the conduction band and lower the gap but a clearly separated deep donor defect level is not found. However, the donor binding energy is still expected to be relatively deep, of order a few 0.1 eV in the hydrogenic effective mass approximation.

The intensity and direction of the electric field effects on off-center shallow-donor impurity binding energy in wedge-shaped cylindrical quantum dots

• In the effective mass approximation, the finite difference method is adopted. • Electric field effect on donor binding energy in a wedge quantum dot is obtained. • The geometrical parameters effects (radius, height and opening) have been affected. • The six confined electronic states dependent on dot shape have been examined. Taking into account an infinite confinement potential, including the influence of external electric field applied in different directions, we have systematically examined the different factors that lead to changes in the ground state binding energy between the hydrogen impurity and the electron, which are confined in a wedge-shaped cylindrical quantum dot (WSCQD) of radius R , height H and azimuthal angle θ m . The resolution of the Schrödinger equation in three dimensions is achieved by the numerical finite difference method. The binding energy is calculated for several quantum dot geometry, various electric field direction, and different position of the impurity located on the first rectangular surface or inside the WSCQD. We have obtained that the direction of the electric field has an important influence on the binding energy of the off-center impurity. We have discussed in detail the weak effect of the radial electric field in the critical value of the WSCQD azimuthal angle θ m = 76.20 ∘ for R = 30 nm and H = 50 nm. The competition between the different effects, such as the electric field direction, the impurity position, and the no-symmetry of the WSCQD, on the electron-impurity distance, is physically interpreted in this paper. To make a more self-contained work, the finite confinement potential effects have also been discussed. Calculations have also been validated by using the finite element method.

Combined effects of hydrostatic pressure and electric field on the donor binding energy, polarizability, and photoionization cross-section in double GaAs/Ga$$_{1-x}$$Al$$_{x}$$As quantum dots

Combined effects of hydrostatic pressure and electric field on the donor binding energy, polarizability, and photoionization cross-section in double GaAs/Ga$$_{1-x}$$Al$$_{x}$$As quantum dots

Donor binding energies in single ZnCdO/ZnO quantum well

The single wurtzite Zn1−xCdxO/ZnO quantum well structure in polar c-direction is studied and the binding energies of an impurity donor atom are obtained. The Schrödinger and Poisson equations are solved self consistently using finite difference method within the effective mass and envelope function approximations. Then, a hydrogenic type of wave function is assumed to represent the impurity, and donor binding energies are obtained using variational approach. The binding energies of the 1s and 2p± states and the transition energy between them are obtained as functions well width, Cd concentration and donor position in the well. Also, an external magnetic field along the growth direction up to 10T is applied to compute the changes in the binding energies. The built-in electric field causes an asymmetric band profile and a triangular well structure, and makes the binding energy curves lose symmetry. The binding energy increases with the donor position as the donor gets close to the wave function penetrated mostly inside the barrier. The built-in electric field is 2.5MV/cm in a 20− Å well with the Cd concentration of x=0.1, and the transition energy is 27.7meV(6.7THz) when the donor is at the well barrier interface close to the electron wave function, but it is 15.7meV(3.8THz) when the donor is at the well center. Also, the Zeeman splitting between the 2p− and 2p+ states is 4.64meV at 10T independent from the donor position.

Effect of electric field on the binding energy and polarisation of shallow donor in a GaAs/Ga1-xAlxAs pillbox surrounded by Ga1-yAlyAs

ABSTRACT Using a variational method in the effective mass approximation, we calculated the binding energy and polarisation of a shallow donor in a GaAs-Ga1-xAlxAs pillbox surrounded by Ga1-yAlyAs. We present our results as a function of the impurity positions and the strength of the electric field for different shapes of the pillbox with constant volume. It is found that the binding energy and polarisation of donor impurity depend strongly on the shape of the pillbox, the position of the impurity, the intensity of the electric field and the thickness of the potential barrier.

Impact of the positive electron–hole exchange interaction constant on the binding energy of neutral donor bound excitons in AlN

Low-temperature photoluminescence spectroscopy is performed for unintentionally doped and silicon-doped aluminum nitride (AlN) films grown on AlN substrates. Considering the positive electron–hole exchange interaction constant substantially changes the neutral silicon-donor bound exciton binding energy from 28.5 to 15.3 meV. The silicon-donor binding energy is also experimentally deduced as 64.8 meV from a two-electron transition, which is justified by a theoretical calculation considering the crystal anisotropy and electron–phonon coupling. The estimated binding energies are discussed with a previous theoretical result within the effective mass approximation and the experimentally known binding energy of elementary four-particle (three-particle) systems.

Tunable tunnel barriers in a semiconductor via ionization of individual atoms

We report scanning tunneling microscopy (STM) studies of individual adatoms deposited on an InSb(110) surface. The adatoms can be reproducibly dropped off from the STM tip by voltage pulses, and impact tunneling into the surface by up to ∼100×. The spatial extent and magnitude of the tunneling effect are widely tunable by imaging conditions such as bias voltage, set current and photoillumination. We attribute the effect to occupation of a (+/0) charge transition level, and switching of the associated adatom-induced band bending. The effect in STM topographic images is well reproduced by transport modeling of filling and emptying rates as a function of the tip position. STM atomic contrast and tunneling spectra are in good agreement with density functional theory calculations for In adatoms. The adatom ionization effect can extend to distances greater than 50 nm away, which we attribute to the low concentration and low binding energy of the residual donors in the undoped InSb crystal. These studies demonstrate how individual atoms can be used to sensitively control current flow in nanoscale devices.

Simultaneous effects of temperature, pressure, polaronic mass, and conduction band non-parabolicity on a single dopant in conical GaAs-Al x Ga1–x As quantum dots

This paper is devoted to the theoretical study of the simultaneous effects of temperature, hydrostatic pressure, conduction band non-parabolicity, and polaronic mass on the electronic states and the photoionization cross-section of a shallow donor impurity confined in a GaAs-Al x GaAs conical quantum dot. The calculations have been made within the effective mass approximation. The shallow donor impurity energy levels have been calculated by employing two methods: the variational approach and the finite element method with finite and infinite confining potential. The obtained results suggest that the effects of conduction band non-parabolicity, temperature, hydrostatic pressure, and variation of the conical quantum dot geometries play a significant role in determining of the electronic states system, as well as in the photoionization cross-section. It is also shown that the donor binding energy is very sensitive to temperature and hydrostatic pressure. Indeed, the temperature decreases the donor binding energy while it is increasing with the applied hydrostatic pressure. Also, the quantum dot effective gap is severely affected by the conduction band non-parabolicity. In the case of polaronic mass effects, the present study suggests that they can be omitted without significantly affecting the study’s main conclusions. In this paper, structures with an apical angle ranging from 10° to 150° are approached, allowing simulating quantum dots with a radius of the base much greater than the height and structures with a height much greater than the radius of the base. In the case of hydrostatic pressure and for quantum dots with finite confinement potential, the Γ-X crossover effect has been considered, which is responsible for significant changes in the carriers’ confinement potential.

Optical properties of spherical quantum dot in the presence of donor impurity under the magnetic field

In this study, the binding energies of an on-center and off-center hydrogenic donor impurity in a spherical quantum dot with finite confinement potential under an applied external magnetic field are investigated in detail by using the matrix diagonalization method in the effective mass approximation. Depending on the calculated energies and wave functions, the linear, third-order nonlinear and total optical absorption coefficients between the ground and several excited states are examined by the iterative method in the compact density matrix approximation for the two-level system. The combined effect of donor position, magnetic field and dot size on binding energies and optical absorption coefficients is observed. The results show that these effects cause significant changes on donor binding energy and optical absorption coefficients.

Magnetic field induced donor binding energy of a GaN/AlGaN quantum dot

Abstract The donor binding energy of a parabolic quantum dot is investigated in the presence of a intense magnetic field. We also consider that the donor is placed at the center of the parabolic quantum dot. Using the effective-mass approximation within a variational scheme, binding energy of donor are obtained as a function of the dot size with and without the magnetic field strength. The result shows that binding energy decreases as the radius of the quantum dot increases or the magnetic field decreases. The magnetic field is appreciable especially for large QD while for small QD the geometrical confinement is predominant.

Laser field effect on self-polarization of a donor impurity in a finite [formula omitted] quantum well

The self-polarization and donor binding energy are calculated for a square Ga1−xAlxAs/GaAs quantum well under an laser field. The donor binding energy and self-polarization are obtained as a function of the laser field parameter, donor impurity position and quantum well-width. The calculations are made by means of variational and finite differences methods using the effective-mass approximation. Our results show that the laser field has remarkable effect on the self-polarization and donor binding energy. These results can be useful for studies on the electronic and optical properties of a quantum well under the influence of a laser field.