Nanofios de arseneto de gálio e arseneto de alumínio

Abstract

We present a first principle study of both bulk e nanowire phases of GaAs and AlAs. We first reproduced the known properties of the bulk materials and then applied the same methodology to study the properties with the dimensional reduction in the nanowires. We determined the variation of the band gap with the composition of "alloys" the nanowires, Al x Ga 1-x As. We also determined the band offset of the heterojunction GaAs/AlAs. We employed the density functional theory, within the local density approximation, to resolve the Kohn-Sham equations and to determine the eigenvalues and total energy of the systems. Nanowires GaAs and AlAs and their alloys AlGaAs, grown in the [111] direction which approximately 19 A diameter, have been simulated using supercells contained 194 atoms. The supercells for the GaAs/AlAs heterojunction contain 388 atoms. After the equilibrium geometry and the electronic density of the ground state were found, we determined the values of the band gap and the average electrostatic potential for the nanowires and their alloys, as well as the value of the average electrostatic potential in the heterojunction. With the value average electrostatic potential it was possible to determine the value of the band offset and the kind of alignment of the heterojunction. Our results show that the dimensional reduction modifies the values of the band gap of the studied materials due the quantum confinement, with a larger variation occurred for the GaAs because of its lower effective mass. The variation of the band gap of the AlGaAs alloy follows very closely the Vegard’s Law. We found a type I band alignment for the bulk and for the nanowires.