Tese
Estudo de primeiros princípios de nanofios em arseneto de índio e fosfeto de índio
Fecha
2011-07-29Registro en:
SANTOS, Cláudia Lange dos. First principles study of indium arsenide and indium phosphide nanowires. 2011. 191 f. Tese (Doutorado em Física) - Universidade Federal de Santa Maria, Santa Maria, 2011.
Autor
Santos, Cláudia Lange dos
Institución
Resumen
In this work we used the density functional theory to study InAs and InP nanowires
and InAs/InP nanowire heterostructures. Initially we studied the structural, electronic
and mechanical properties of InAs and InP nanowires as a function of the diameter and the
influence of external mechanical stress on the electronic properties of these systems. Our
results show that all analyzed properties change with increasing quantum confinement.
Further, the application of an external stress along the nanowire axis reveals a direct to
indirect band gap transition for compressive strain in very thin nanowires.
We have also studied the quantum confinement effects on the effective masses of
charge carriers in InAs nanowires grown in different crystallographic directions. We found
the electron and hole effective masses increase with decreasing diameter independently of
the growth direction. However, in the range of the studied diameters, the hole effective
mass is significantly smaller to the corresponding one at the bulk system.
From the study of the stability and electronic properties of the cadmium and zinc
doped InAs nanowires, we show that the Cd impurity prefers to be at the core region,
whereas Zn impurity is found to be equally distributed along the nanowire diameter. The
analysis of the electronic properties of these systems show that these impurities introduce
shallow acceptor levels in the band gap, enabling a p-type behavior of these nanowires.
Finally, we determined (i) the structural, electronic and mechanical properties of
axially and radially modulated InAs/InP nanowire heterostructures for a specific diameter
and (ii) the structural and electronic properties of radial InAs/InP nanowire heterostructures
as a function of the diameter and composition. From (i), our calculations showed
the analyzed properties have an intermediate value between those for the pure InAs and
InP nanowires with similar diameters. In particular, the presence of an InP shell covering
the InAs nanowires enhances the InAs electron mobility, as compared to the uncapped
InAs nanowires. In addition, for the radial heterostructure, the conduction and the valence
band alignments favor a type-I heterojunction, while for the axial heterostructure
a transition from a type-I to a type-II heterojunction could occur at this range of diameters.
From (ii), we observed that for nanowire heterostrutures of similar diameters,
the variation of their structural and electronic properties with the composition possesses
significant deviations from the linear behavior, which are dependent of the nanostructure
diameter. The conduction band offset is approximately zero and the valence band offset
decrease regardless of diameter and composition of the heterostructure.