Confinamento dielétrico versus quântico em nanoestruturas

Abstract

We study in this work the low dimensional quantum well systems (QW) of GaN/HfO2 and Si/High − k. In GaN/HfO2 QW, we analyze not only the electronic and optic properties but also impurity states of this system. Moreover, we consider the image charge effects. This is due to discontinuity of materials dielectric constant of well (εw) and barriers (εb) of this structures. At first, we analyze the image potential effects of selfenergy in electronic and optic proprieties of abrupt and non-abrupt QWs. We observed that the electronic structure of QW is strongly modified by the image potential effect of self-energy. It is found that the recombination energy of carriers can change up to 100 meV. Moreover, we observed that the ideal model (En ∼ n 2/L2) of QWs is not valid for some structures with εw < εb due to confinement of carries in the interface. Second, exciton binding and exciton total energy in εw < εb and εw > εb abrupt QWs are studied giving more importance on effect caused by image charges, for example, self energy potential and interactions among electron (hole) and the image charges of hole (electron). Considering the materials and parameters used in this work, we observed that simple models used to evaluate exciton, which do not consider image charge effects, are not appropriated to study systems with εw < εb since appropriated models, which consider all image charge effects, present results with significative changes, around 80 meV, with regard to the simplest models. Finally, impurity states are studied in abrupt GaN/HfO2 QWs. We considered all the energy contributions caused by the change between the dielectric constant of GaN (εGaN =9.5) and HfO2 (εHfO2 =25) simultaneously. The results show that, as the impurity is dislocated toward the interface, the electron wave function is attracted in the same direction. The attraction intensity decreases when the impurity moves to far from interface in the barrier region.