Craig E. Pryor

Eight-band calculations of strained InAs/GaAs quantum dots compared with one-, four-, and six-band approximations

The electronic structure of pyramidal shaped InAs/GaAs quantum dots is calculated using an eight-band strain-dependent

Comparison of two methods for describing the strain profiles in quantum dots

\mathbf{k}\ensuremath{\cdot}\mathbf{p}

Predicted band structures of III-V semiconductors in the wurtzite phase

Hamiltonian. The influence of strain on band energies and the conduction-band effective mass are examined. Single-particle bound-state energies and exciton binding energies are computed as functions of island size. The eight-band results are compared with those for one, four, and six bands, and with results from a one-band approximation in which

Band-edge diagrams for strained III-V semiconductor quantum wells, wires, and dots

{m}_{\mathrm{eff}}(\stackrel{\ensuremath{\rightarrow}}{r})

Excited states of individual quantum dots studied by photoluminescence spectroscopy

is determined by the local value of the strain. The eight-band model predicts a lower ground-state energy and a larger number of excited states than the other approximations.

Direct Measure of Strain and Electronic Structure in GaAs/GaP Core−Shell Nanowires

The electronic structure of interfaces between lattice-mismatched semiconductors is sensitive to the strain. We compare two approaches for calculating such inhomogeneous strain—continuum elasticity [(CE), treated as a finite difference problem] and atomistic elasticity. While for small strain the two methods must agree, for the large strains that exist between lattice-mismatched III-V semiconductors (e.g., 7% for InAs/GaAs outside the linearity regime of CE) there are discrepancies. We compare the strain profile obtained by both approaches (including the approximation of the correct C2 symmetry by the C4 symmetry in the CE method) when applied to C2-symmetric InAs pyramidal dots capped by GaAs.

QUANTUM WIRES FORMED FROM COUPLED INAS/GAAS STRAINED QUANTUM DOTS

While non-nitride III-V semiconductors typically have a zinc-blende structure, they may also form wurtzite crystals under pressure or when grown as nanowhiskers. This makes electronic structure calculation difficult since the band structures of wurtzite III-V semiconductors are poorly characterized. We have calculated the electronic band structure for nine III-V semiconductors in the wurtzite phase using transferable empirical pseudopotentials including spin-orbit coupling. We find that all the materials have direct gaps. Our results differ significantly from earlier ab initio calculations, and where experimental results are available (InP, InAs, and GaAs) our calculated band gaps are in good agreement. We tabulate energies, effective masses, and linear and cubic Dresselhaus zero-field spin-splitting coefficients for the zone-center states. The large zero-field spin-splitting coefficients we find may facilitate the development of spin-based devices.

Calculations of the electronic structure of strained InAs quantum dots in InP

We have calculated band-edge energies for most combinations of zinc blende AlN, GaN, InN, GaP, GaAs, InP, InAs, GaSb, and InSb in which one material is strained to the other. Calculations were done for three different geometries (quantum wells, wires, and dots) and mean effective masses were computed in order to estimate confinement energies. For quantum wells, we have also calculated band-edges for ternary alloys. Energy gaps, including confinement, may be easily and accurately estimated using band energies and a simple effective mass approximation, yielding excellent agreement with experimental results. By calculating all material combinations we have identified interesting material combinations, such as artificial donors, that have not been experimentally realized. The calculations were perfomed using strain-dependent k center dot p theory and provide a comprehensive overview of band structures for strained heterostructures. (Less)

Electronic structure of strained I n P / G a 0.51 In 0.49 P quantum dots

The photoluminescence from individual InP quantum dots embedded in a matrix of GaInP has been studied. In addition to the ground state emission that consists of several peaks, we observe excited states of the dot. These states are observed either via state filling or with photoluminescence excitation spectroscopy. We observe a fast relaxation to the set of states with lowest energy but no relaxation between these states.

Accuracy of Circular Polarization as a Measure of Spin Polarization in Quantum Dot Qubits

Highly strained GaAs/GaP nanowires of excellent optical quality were grown with 50 nm diameter GaAs cores and 25 nm GaP shells. Photoluminescence from these nanowires is observed at energies dramatically shifted from the unstrained GaAs free exciton emission energy by 260 meV. Using Raman scattering, we show that it is possible to separately measure the degree of compressive and shear strain of the GaAs core and show that the Raman response of the GaP shell is consistent with tensile strain. The Raman and photoluminescence measurement are both on good agreement with 8 band k.p calculations. This result opens up new possibilities for engineering the electronic properties of the nanowires for optimal design of one-dimensional nanodevices by controlling the strain of the core and shell by varying the nanowire geometry.