There are a variety of methods available for confining and manipulating single spins in solid state systems. While heterostructures can be engineered to the requirements of the problem, their variability is a disadvantage compared to identical impurities. I will discuss theoretical calculations of electronic states in both quantum dot heterostructures and bound to impurities. These include calculations of the spin state itself, the effective coupling to a magnetic field, the response to an electric field, and include both electrons and holes.
The electronic structure of isoelectronic defects, donors and acceptors is calculated within a full superlattice
picture for InAs/GaSb and InAs/GaInSb superlattices. The wavefunctions associated with these states extend
beyond a typical layer width for the superlattices. Thus band alignments between the layers as well as interface
properties are predicted to dramatically change these defects' binding energy as well as their influence on superlattice
electronic, optical and transport properties. Defect properties are also substantially modified by their
location within a superlattice layer.
In systems with sizable spin-orbit interaction intense optical illumination or an electric field can generate an
effective "pseudomagnetic field" which replaces a true applied magnetic field for the efficient and rapid manipulation
of spins. The theoretical characteristics of optically-induced spin precession in self-assembled quantum
dots will be described, along with the potential for manipulating spins bound to donors and acceptors with
Manipulating individual spins in a solid, such as for quantum information processing or a spintronic device, requires the ability to quickly and coherently reorient a spin while leaving its neighbors unaffected.
Using traditional electron spin resonance methods is problematic because of the difficulty of confining oscillating magnetic fields to small volumes.
In contrast, g-tensor modulation resonance, which has been demonstrated in quantum wells, uses the electric field to exploit differences in the spin-orbit interaction in and around the confining structure and should be scalable.
I will present theoretical calculations of g-tensor modulation resonance spin manipulation in quantum dots and donors and show that such schemes are feasible for manipulation of single spins.
For InAs/GaAs quantum dots it is possible to rapidly reorient the spin in an arbitrary direction with only the application of a static magnetic field and the application of pulsed electric fields from a gate.
Donors behave much like quantum dots, with the advantage that they do not suffer from variations in composition and size.
We propose core-shell nanorods such as InP-CdS and InP-ZnTe to be photoelectrodes for efficient photoelectrochemical
hydrogen production. Based on our systematic study using strain-dependent <i>k.p</i> theory, we find that in these
heterostructures both energies and wave-function distributions of electrons and holes can be favorably tailored to a
considerable extent by exploiting the interplay between quantum confinement and strain. Consequently, these core-shell
nanorods with proper dimensions (height, core radius, and shell thickness) may simultaneously satisfy all criteria for
effective photoelectrodes in solar-based hydrogen production.
Serpentine superlattices (SSL) with a parabolic-crescent cross section defining the wells and barriers, have been grown on vicinal GaAs substrates by molecular beam epitaxy. The SSL structures have been studied by photoluminescence (PL) and photoluminescence excitation (PLE) measurements at 1.4 K, showing a strong polarization anisotropy in both PL and PLE. The carrier confinement has been characterized by measuring the linear polarization dependence of the PL from the surface as well as from the cleaved edges by using a photoelastic modulation technique. Calculations of the conduction band and valence band electronic structure describe the polarization dependence as a function of segregation into lateral wells and barriers. We find that about 30% of the Al intended for the barriers end up in the well giving Al<SUB>x</SUB>Ga<SUB>1-x</SUB>As wells and barriers of x equals 0.12 and 0.21, instead of the nominally intended values of 0.00 and 0.33, corresponding to a lateral conduction band barrier of 70 meV. Linear polarized PLE has been used to reveal the laterally induced heavy-light hole splitting. PL decay time measurements of the serpentine emission, shows a longer decay time than for a reference alloy-well structure, indicating a reduced carrier relaxation in the serpentine structure. The linear polarization of the PL is found to be rather constant over large areas of the wafer indicating uniform quantum wire like states, showing the intended advantage of the serpentine structure over tilted superlattices.