Um polarizador de spin de dupla barreira

Abstract

In this thesis it is developed a theoretical model for a nanoscopic device based on studies of diluted magnetic semiconductors (DMS) and transport in semiconducting heterostructures. The main motivation for working with this project is to make a contribution for the development of spintronics which has the purpose of exploiting spin degrees of freedom of particles as well as their charges. This area of physics has received much attention because it can be a basis for quantum computing in the future. The device consists of semiconducting heterostructures made from layers of Ga1-xMnxAs and Ga1-yAlyAs. Ga1-xMnxAs is, at low temperatures and for some values of x, a ferromagnetic semiconductor. It was made a study of double barrier resonant tunneling for heavy holes (HH) and light holes (LH). The calculations were made in the tight-binding approximation and the interaction between holes was calculated in the Hartree approximation. It was used a decimation formalism for the treatment of the spatial component of the SchrÄodinger equation perpendicular to the material interfaces. Furthermore, charge distribution and potential energy profile were calculated selfconsistently. We have analyzed the current of holes and the resonant levels of the well (created by the double barrier) for the device, under a variable applied voltage and without external magnetic field. In the proposed model, we have observed that hole distribution is essentially made of HH and the magnetism is also sustained by HH. Furthermore, from the study of how charge distribution and potential profile evolve under a variable applied voltage, we could develop well optimized numerical methods. We have also observed the existance of two distinct regimes for the evolution of the potencial energy profile. Finally, we obtained spin polarized currents for LH.