ZnTe/CdSe type-II core/shell spherical quantum dot under an external electric field

International audienceWe have investigated in the framework of the envelope function approximation and taking into account the dependence of the electron effective mass on radius the energy of an electron inside a ZnTe/CdSe core/shell spherical quantum dot. In order to make the problem more realistic, we describe the conduction band-edge alignment between core and shell materials by a finite height barrier. By applying the Ritz variational principle the effect of the electric field on the electronic states was also examined. Our numerical results show the opportunity to control the energy states position of the charge carriers inside our core/shell nanostructures by controlling the size (core radius, shell thickness) of the nanostructure and the strength of the external electric field

Influence of long-range dipolar interactions on the phase stability and hysteresis shapes of ferroelectric and antiferroelectric multilayers

Phase transition and field driven hysteresis evolution of a two-dimensional Ising grid consisting of ferroelectric-antiferroelectric multilayers that take into account the long range dipolar interactions were simulated by a Monte-Carlo method. Simulations were carried out for a 1+1 bilayer and a 5+5 superlattice. Phase stabilities of components comprising the structures with an electrostatic-like coupling term were also studied. An electrostatic-like coupling, in the absence of an applied field, can drive the ferroelectric layers towards 180º domains with very flat domain interfaces mainly due to the competition between this term and the dipole-dipole interaction. The antiferroelectric layers do not undergo an antiferroelectric-to-ferroelectric transition under the influence of an electrostatic-like coupling between layers as the ferroelectric layer splits into periodic domains at the expense of the domain wall energy. The long-range interactions become significant near the interfaces. For high periodicity structures with several interfaces, the interlayer long-range interactions substantially impact the configuration of the ferroelectric layers while the antiferroelectric layers remain quite stable unless these layers are near the Neel temperature. In systems investigated with several interfaces, the hysteresis loops do not exhibit a clear presence of antiferroelectricity that could be expected in the presence of anti-parallel dipoles, i. e., the switching takes place abruptly. Some recent experimental observations in ferroelectric-antiferroelectric multilayers are discussed where we conclude that the different electrical properties of bilayers and superlattices are not only due to strain effects alone but also long-range interactions. The latter manifests itself particularly in superlattices where layers are periodically exposed to each other at the interfaces

Linear and nonlinear optical properties of donors inside a CdSe/ZnTe core/shell nanodot : Role of size modulation

The optical absorption coefficient (OAC) and the refractive index (RI), related to a confined donor, were theoretically investigated by the mean of the density matrix formalism. In order to obtain the 1s - 1p donor transition energy a variational calculation, within the context of the effective-mass approach, was deployed. Our numerical results exhibit the possibility to modulate the electronic and optical properties of confined donors by tailoring the inner and outer radii of the core/shell heterodot. Further, we have obtained that the nanodot size shrinking leads, for very small values of core radius, to reduce the magnitude of the total absorption coefficient resonance peak. It was also obtained that the resonance peak position of the absorption coefficient is redshifted with increasing the core radius for a fixed shell thickness. The same situation occurs when reducing the thickness of the shell material for a fixed core size