106 research outputs found
An electronic model for self-assembled hybrid organic/perovskite semiconductors: reverse band edge electronic states ordering and spin-orbit coupling
Based on density functional theory, the electronic and optical properties of
hybrid organic/perovskite crystals are thoroughly investigated. We consider the
mono-crystalline 4FPEPI as material model and demonstrate the optical process
is governed by three active Bloch states at the {\Gamma} point of the reduced
Brillouin zone with a reverse ordering compared to tetrahedrally bonded
semiconductors. Giant spin-orbit coupling effects and optical activities are
subsequently inferred from symmetry analysis.Comment: 17 pages, 6 figure
Optical properties of potential-inserted quantum wells in the near infrared and Terahertz ranges
We propose an engineering of the optical properties of GaAs/AlGaAs quantum
wells using AlAs and InAs monolayer insertions. A quantitative study of the
effects of the monolayer position and the well thickness on the interband and
intersubband transitions, based on the extended-basis sp3d5s* tight-binding
model, is presented. The effect of insertion on the interband transitions is
compared with existing experimental data. As for intersubband transitions, we
show that in a GaAs/AlGaAs quantum well including two AlAs and one InAs
insertions, a three level {e1 , e2 , e3 } system where the transition energy
e3-e2 is lower and the transition energy e2-e1 larger than the longitudinal
optical phonon energy (36 meV) can be engineered together with a e3-e2
transition energy widely tunable through the TeraHertz range
Free-carrier screening of polarization fields in wurtzite GaN/InGaN laser structures
The free-carrier screening of macroscopic polarization fields in wurtzite
GaN/InGaN quantum wells lasers is investigated via a self-consistent
tight-binding approach. We show that the high carrier concentrations found
experimentally in nitride laser structures effectively screen the built-in
spontaneous and piezoelectric polarization fields, thus inducing a
``field-free'' band profile. Our results explain some heretofore puzzling
experimental data on nitride lasers, such as the unusually high lasing
excitation thresholds and emission blue-shifts for increasing excitation
levels.Comment: RevTeX 4 pages, 4 figure
Intrinsic interface states in InAs-AlSb heterostructures
We examine the possibility of intrinsic interface states bound to the plane
of In-Sb chemical bonds at InAs/AlSb interfaces. Careful parameterization of
the bulk materials in the frame of the extended basis spds^* tight-binding
model and recent progress in predictions of band offsets severely limit the
span of tight-binding parameters describing this system. We find that a
heavy-hole like interface state bound to the plane of In-Sb bonds exists for a
large range of values of the InSb/InAs band offset
Anisotropic magneto-resistance in a GaMnAs-based single impurity tunnel diode: a tight binding approach
Using an advanced tight-binding approach, we estimate the anisotropy of the
tunnel transmission associated with the rotation of the 5/2 spin of a single Mn
atom forming an acceptor state in GaAs and located near an AlGaAs tunnel
barrier. Significant anisotropies in both in-plane and out-of-plane geometries
are found, resulting from the combination of the large spin-orbit coupling
associated with the p-d exchange interaction, cubic anisotropy of heavy-hole
dispersion and the low C2v symmetry of the chemical bonds.Comment: 4 pages, 3 figure
Realistic Tight Binding Model for the Electronic Structure of II-VI Semiconductors
We analyze the electronic structure of group II-VI semiconductors obtained
within LMTO approach in order to arrive at a realistic and minimal tight
binding model, parameterized to provide an accurate description of both valence
and conduction bands. It is shown that a nearest-neighbor model is
fairly sufficient to describe to a large extent the electronic structure of
these systems over a wide energy range, obviating the use of any fictitious
orbital. The obtained hopping parameters obey the universal scaling law
proposed by Harrison, ensuring transferability to other systems. Furthermore,
we show that certain subtle features in the bonding of these compounds require
the inclusion of anion-anion interactions in addition to the nearest-neighbor
cation-anion interactions.Comment: 9 pages, 9 figure
STM images of sub-surface Mn atoms in GaAs: evidence of hybridization of surface and impurity states
We prove that scanning tunneling microscopy (STM) images of sub-surface Mn
atoms in GaAs are formed by hybridization of the impurity state with intrinsic
surface states. They cannot be interpreted in terms of bulk-impurity
wavefunction imaging. High atomic resolution images obtained using a
low-temperature apparatus are compared with advanced, parameter-free
tight-binding simulations accounting for both the buckled (110) surface and
vacuum electronic properties
Nonparabolicity effects and the spin-split electron dwell time in symmetric III-V double-barrier structures
We start from the fourth order nonparabolic and anisotropic conduction band bulk dispersion relation to obtain an one-band effective Hamiltonian which we apply to an AlGaSb symmetric double-barrier structure with resonant energies significantly (more than 200meV) above the well bottom. The spin-splitting is described by the k3 Dresselhaus spin-orbit coupling term modifying only the effective mass of the spin eigenstates in the investigated structure. Apart from the bulk-like resonant energy shift due to the band nonparabolicity, we obtain a substantial shift depending on the choice of boundary conditions for the envelope functions at interfaces between different materials. The shift of resonant energy levels leads to the change of spin-splitting and the magnitude of the dwell times. We attempt to explain the influence of both the nonparabolicity and boundary conditions choice by introducing various effective masses
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