Simultaneous effects of pressure and temperature on donors in a GaAlAs/GaAs quantum well

The ground state and a few excited state energies of a hydrogenic donor in a quantum well are computed in the presence of pressure and temperature. The binding energies are worked out for GaAs/ Ga_1−xAl_xAs structures as a function of well size when the pressure and temperature are applied simultaneously. A variational approach within the effective mass approximation is considered. The results show that for a constant applied pressure, an increase in temperature results in a decrease in donor impurity binding energy while an increase in the pressure for the same temperature enhances the binding energy. When the pressure and temperature are applied simultaneously the binding energy decreases as the well width increases. In all the cases, it is observed that there is an increase in the binding energy due to the decrease in the quantum well size and in the dielectric constant whereas the effects of temperature on the effective mass are minimal.     

$$ \mathcal{I}_g $$-normal and $$ \mathcal{I}_g $$-regular spaces

$ \mathcal{I}_g $ \mathcal{I}_g -normal and $ \mathcal{I}_g $ \mathcal{I}_g -regular spaces are introduced and various characterizations and properties are given. Characterizations of normal, mildly normal, g-normal, regular and almost regular spaces are also given.     

<Emphasis Type="Italic">g</Emphasis>-closed sets in ideal topological spaces

Characterizations and properties of $ \mathcal{I}_g $ \mathcal{I}_g -closed sets and $ \mathcal{I}_g $ \mathcal{I}_g -open sets are given. A characterization of normal spaces is given in terms of $ \mathcal{I}_g $ \mathcal{I}_g -open sets. Also, it is established that an $ \mathcal{I}_g $ \mathcal{I}_g -closed subset of an $ \mathcal{I} $ \mathcal{I} -compact space is $ \mathcal{I} $ \mathcal{I} -compact.     

Effects of electric field and hydrostatic pressure on donor binding energies in a spherical quantum dot

The binding energies of a hydrogenic donor in a GaAs spherical quantum dot in the Ga_1−xAl_xAs matrix are presented assuming parabolic confinement. Effects of hydrostatic pressure and electric field are discussed on the results obtained using a variational method. Effects of the spatial variation of the dielectric screening and the effective mass mismatch are also investigated. Our results show that (i) the ionization energy decreases with dot size, with the screening function giving uniformly larger values for dots which are less than about 25 nm, (ii) the hydrostatic pressure increases the donor ionization energy such that the variation is larger for a smaller dot, and (iii) the ionization energy decreases in an electric field. All the calculations have been carried out with finite barriers and good agreement is obtained with the results available in the literature in limiting cases.     

Combined effects of electric and magnetic fields on confined donor states in a diluted magnetic semiconductor parabolic quantum dot

A variational formalism for the calculation of the binding energies of hydrogenic donors in a parabolic diluted magnetic semiconductor quantum dot is discussed. Results are obtained for Cd Mn Te/Cd Mn Te structures as a function of the dot radius in the presence of external magnetic and electric fields applied along the growth axis. The donor binding energies are computed for different field strengths and for different dot radii. While the variation of impurity binding energy with dot radii and electric field are as expected, the polarizability values enhance in a magnetic field. However, for certain values of dot radii and in intense magnetic fields the polarizability variation is anomalous. This variation of polarizability is different from non- magnetic quantum well structures. Spin polaronic shifts are estimated using a mean field theory. The results show that the spin polaronic shift increases with magnetic field and decreases as the electric field and dot radius increase.     

Hydrogenic Donor in a Spherical Quantum Dot with Different Confinements

Binding energies of a hydrogenic donor in a spherical GaAs quantum dot surrounded by Ga1-xA4xAs matrix are calculated. The results are presented for realistie barrier heights corresponding to different values of x （x 〈 0.4）. The calculations are performed under two different conditions： （i） a spherical dot with square well confinement and （ii） a dot with parabolic potential well confinement. The results show that （i） the donor ionization energies are always higher under parabolic confinement as compared to a dot of the same radius under square well confinement and （ii） the oscillator strengths coupling ground state with excited states are two orders larger under parabolic confinement. Our results are in agreement with the results of other researchers.     

Spin-polarized transport through a time-periodic non-magnetic semiconductor heterostructure

Spin-dependent Floquet scattering theory is developed to investigate the photon-assisted spin-polarized electron transport through a semiconductor heterostructure in the presence of an external electric field. Spin-dependent Fano resonances and spin-polarized electron transport through a laser irradiated time-periodic non-magnetic heterostructure in the presence of Dresselhaus spin-orbit interaction and a gate-controlled Rashba spin-orbit interaction are investigated. The electric field due to laser along with the spin-orbit interactions help to get spin-dependent Fano resonances in the conductance, whereas the external bias can be appropriately adjusted to get a near 80% spin-polarized electron transmission through heterostructures. The resultant nature of the Floquet scattering depends on the relative strength of these two electric fields.     

Phonon–polariton in a piezoelectric superlattice

In a series of works Zhu et al. [Phy. Rev.Lett. 90 (2003) 0532903] have investigated the possibility of acoustic polaritons in a novel superlattice system consisting of piezoelectric materials. In the present work that two excitations are pointed out are: one due to piezo polaritons and the other due to the optic phonon mode. The behavior of the photonic gaps as a function of superlattice period is investigated systematically.     

Semiconductor to metal transition in strictly two dimension–a comparative study on GaAs and carbon nanotube

Choosing GaAs, donor binding energies in two dimension are obtained using Thomas–Fermi and Hartree screening functions within the effective mass approximation. Binding energies are computed both in the hydrogen atom model and D ^? ion model. The results show the non-feasibility of semiconductor-to-metal transition (SMT) in two-dimensional system of GaAs. For curiosity we have obtained the donor binding energies in carbon nanotube (CNT), a highly correlated system by considering it as two-dimensional structure. We could observe the feasibility of SMT in CNT. This indicates the strong confinement in nanostructures and the results will be useful for nanodevice fabrication.