483 research outputs found
Spin-polarized multiexcitons in quantum dots in the presence of spin-orbit interaction
An efficient electron spin-relaxation mechanism has been observed in InAs quantum dots (QDs) that manifests itself as a sharp drop in the circular polarization of the light emitted by Fe spin-light emitting diodes, which incorporate a single layer of InGaAs QDs, for a narrow range of magnetic fields around 5 T. The underlying mechanism occurs when the QDs are occupied by three-electron-hole pairs forming a tri-exciton (3X) and is a two-step process. The first step involves the spin flip of one of the three electrons mediated by the spin-orbit interaction; in the second step the 3X relaxes to its ground state via phonon emission
Determination of Interface Atomic Structure and Its Impact on Spin Transport Using Z-Contrast Microscopy and Density-Functional Theory
We combine Z-contrast scanning transmission electron microscopy with
density-functional-theory calculations to determine the atomic structure of the
Fe/AlGaAs interface in spin-polarized light-emitting diodes. A 44% increase in
spin-injection efficiency occurs after a low-temperature anneal, which produces
an ordered, coherent interface consisting of a single atomic plane of
alternating Fe and As atoms. First-principles transport calculations indicate
that the increase in spin-injection efficiency is due to the abruptness and
coherency of the annealed interface.Comment: 16 pages (including cover), 4 figure
Graphene Schottky diodes: an experimental review of the rectifying graphene/semiconductor heterojunction
In the past decade graphene has been one of the most studied material for
several unique and excellent properties. Due to its two dimensional nature,
physical and chemical properties and ease of manipulation, graphene offers the
possibility of integration with the exiting semiconductor technology for
next-generation electronic and sensing devices. In this context, the
understanding of the graphene/semiconductor interface is of great importance
since it can constitute a versatile standalone device as well as the
building-block of more advanced electronic systems. Since graphene was brought
to the attention of the scientific community in 2004, the device research has
been focused on the more complex graphene transistors, while the
graphene/semiconductor junction, despite its importance, has started to be the
subject of systematic investigation only recently. As a result, a thorough
understanding of the physics and the potentialities of this device is still
missing. The studies of the past few years have demonstrated that graphene can
form junctions with 3D or 2D semiconducting materials which have rectifying
characteristics and behave as excellent Schottky diodes. The main novelty of
these devices is the tunable Schottky barrier height, a feature which makes the
graphene/semiconductor junction a great platform for the study of interface
transport mechanisms as well as for applications in photo-detection, high-speed
communications, solar cells, chemical and biological sensing, etc. In this
paper, we review the state-of-the art of the research on graphene/semiconductor
junctions, the attempts towards a modeling and the most promising applications.Comment: 85 pages. Review articl
Interfaces between nonpolar and semipolar III-nitride semiconductor orientations: Structure and defects
Observations of easy transition between nonpolar and semipolar orientations during III-Nitride
heteroepitaxy identify the 90o rotation relationship as being very important in defining this coexistence. A rigorous analysis of this relationship using the topological theory of interfaces showed that it leads to a high order of coincident symmetry and makes energetically favorable the appearance of the intergranular boundaries. Principal low-energy boundaries, that could also be technologically exploited, have been identified by high-resolution transmission electron microscopy (HRTEM) observations and have been studied energetically using empirical potential calculations. It is also shown that these boundaries can change their average orientation by incorporating disconnections. The pertinent strain relaxation mechanisms can cause such boundaries to act as sources of threading dislocations and stacking faults. The energetically favorable (10-10) // (0001) boundary was frequently observed to delimit m-plane crystallites in (-12-12) semipolar growth
- …