Confinamento em fios quânticos semicondutores

Abstract

Advances in growth techniques have made possible the fabrication of one-dimensional semiconductor nanometric structures, named quantum wires. There has ben an increasing interest in such structures, due to their applicability in electronic devices and also because their chemistry is easily manipulated. In particular, experimental works have reported the growth of core-shell quantum wires and semiconductor wires with longitudinal heterostructures. In this work, the excitonic properties of cylindrical Si/Si1¡xGex core-shell quantum wires are studied, considering two possibilities for the conduction band alignment: type-I, where electrons and holes are confined at the same material, and type-II, where these carriers are spatially separated. We use a Hamiltonian which takes into account the existence of non-abrupt interfaces between materials. For type-I, it is observed that the exciton energy is weakly affected by the presence of a magnetic field, especially for smaller wire radii. For type-II structures, increasing the magnetic field intensity leads to almost periodic changes on the electron angular momentum, which yields to Aharonov-Bohm oscillations on the exciton energy. We also investigate theoretically how the existence of graded interfaces may affect the confinement of carriers in cylindrical GaAs/GaP and InAs/InP quantum wires with single heterostructures along the wire axis. Numerical results show that, when abrupt interfaces are considered, as the wire radius becomes thinner the effective potential acting on a carrier might induce its longitudinal localization at the barriers. However, considering smooth interfaces, this effective potential acquires a peculiar form, in which electron and hole states may be confined inside traps formed at the interfacial regions.