210 research outputs found
Multiband effective bond-orbital model for nitride semiconductors with wurtzite structure
A multiband empirical tight-binding model for group-III-nitride
semiconductors with a wurtzite structure has been developed and applied to both
bulk systems and embedded quantum dots. As a minimal basis set we assume one
s-orbital and three p-orbitals, localized in the unit cell of the hexagonal
Bravais lattice, from which one conduction band and three valence bands are
formed. Non-vanishing matrix elements up to second nearest neighbors are taken
into account. These matrix elements are determined so that the resulting
tight-binding band structure reproduces the known Gamma-point parameters, which
are also used in recent kp-treatments. Furthermore, the tight-binding band
structure can also be fitted to the band energies at other special symmetry
points of the Brillouin zone boundary, known from experiment or from
first-principle calculations. In this paper, we describe details of the
parametrization and present the resulting tight-binding band structures of bulk
GaN, AlN, and InN with a wurtzite structure. As a first application to
nanostructures, we present results for the single-particle electronic
properties of lens-shaped InN quantum dots embedded in a GaN matrix.Comment: 10 pages, 5 figures, two supplementary file
Derivation of phenomenological expressions for transition matrix elements for electron-phonon scattering
In the literature on electron-phonon scatterings very often a
phenomenological expression for the transition matrix element is used which was
derived in the textbooks of Ashcroft/Mermin and of Czycholl. There are various
steps in the derivation of this expression. In the textbooks in part different
arguments have been used in these steps, but the final result is the same. In
the present paper again slightly different arguments are used which motivate
the procedure in a more intuitive way. Furthermore, we generalize the
phenomenological expression to describe the dependence of the matrix elements
on the spin state of the initial and final electron state
A comparison of atomistic and continuum theoretical approaches to determine electronic properties of GaN/AlN quantum dots
In this work we present a comparison of multiband k.p-models, the effective
bond-orbital approach, and an empirical tight-binding model to calculate the
electronic structure for the example of a truncated pyramidal GaN/AlN
self-assembled quantum dot with a zincblende structure. For the system under
consideration, we find a very good agreement between the results of the
microscopic models and the 8-band k.p-formalism, in contrast to a 6+2-band
k.p-model, where conduction band and valence band are assumed to be decoupled.
This indicates a surprisingly strong coupling between conduction and valence
band states for the wide band gap materials GaN and AlN. Special attention is
paid to the possible influence of the weak spin-orbit coupling on the localized
single-particle wave functions of the investigated structure
Optically and electrically controllable adatom spin-orbital dynamics in transition metal dichalcogenides
We analyze the interplay of spin-valley coupling, orbital physics and
magnetic anisotropy taking place at single magnetic atoms adsorbed on
semiconducting transition-metal dichalcogenides, MX (M = Mo, W; X = S, Se).
Orbital selection rules turn out to govern the kinetic exchange coupling
between the adatom and charge carriers in the MX and lead to highly
orbitally dependent spin-flip scattering rates, as we illustrate for the
example of transition metal adatoms with configuration. Our ab initio
calculations suggest that configurations are realizable by single Co, Rh,
or Ir adatoms on MoS, which additionally exhibit a sizable magnetic
anisotropy. We find that the interaction of the adatom with carriers in the
MX allows to tune its behavior from a quantum regime with full Kondo
screening to a regime of "Ising spintronics" where its spin-orbital moment acts
as classical bit, which can be erased and written electronically and optically.Comment: 6 pages, 4 figure
Optical properties of self-organized wurtzite InN/GaN quantum dots: A combined atomistic tight-binding and full configuration interaction calculation
In this work we investigate the electronic and optical properties of
self-assembled InN/GaN quantum dots. The one-particle states of the
low-dimensional heterostructures are provided by a tight-binding model that
fully includes the wurtzite crystal structure on an atomistic level. Optical
dipole and Coulomb matrix elements are calculated from these one-particle wave
functions and serve as an input for full configuration interaction
calculations. We present multi-exciton emission spectra and discuss in detail
how Coulomb correlations and oscillator strengths are changed by the
piezoelectric fields present in the structure. Vanishing exciton and biexciton
ground state emission for small lens-shaped dots is predicted.Comment: 3 pages, 2 figure
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