5,176 research outputs found
Origin of non-linear piezoelectricity in III-V semiconductors: Internal strain and bond ionicity from hybrid-functional density functional theory
We derive first- and second-order piezoelectric coefficients for the
zinc-blende III-V semiconductors, {Al,Ga,In}-{N,P,As,Sb}. The results are
obtained within the Heyd-Scuseria-Ernzerhof hybrid-functional approach in the
framework of density functional theory and the Berry-phase theory of electric
polarization. To achieve a meaningful interpretation of the results, we build
an intuitive phenomenological model based on the description of internal strain
and the dynamics of the electronic charge centers. We discuss in detail first-
and second-order internal strain effects, together with strain-induced changes
in ionicity. This analysis reveals that the relatively large importance in the
III-Vs of non-linear piezoelectric effects compared to the linear ones arises
because of a delicate balance between the ionic polarization contribution due
to internal strain relaxation effects, and the contribution due to the
electronic charge redistribution induced by macroscopic and internal strain
Theory of the electronic structure of dilute bismide and bismide-nitride alloys of GaAs: Tight-binding and k.p models
The addition of dilute concentrations of bismuth (Bi) into GaAs to form
GaBiAs alloys results in a large reduction of the band gap energy Eg
accompanied by a significant increase of the spin-orbit-splitting energy
(delta_SO), leading to an Eg < delta_SO regime for ~10% Bi composition which is
technologically relevant for the design of highly efficient photonic devices.
The quaternary alloy GaBiNAs offers further flexibility for band gap tuning,
because both nitrogen and bismuth can independently induce band gap reduction.
This work reports sp3s* tight binding and 14-band k.p models for the study of
the electronic structure of GaBiAs and GaBiNAs alloys. Our results are in good
agreement with the available experimental data.Comment: 2 pages, 1 figur
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Built-in field reduction in InGaN/GaN quantum dot molecules
We use a tight-binding model to study the electronic structure of InGaN/GaN quantum dot molecules grown along the c-axis. This analysis is carried out as a function of the barrier thickness between the two non-identical dots. Our results show that the built-in field is effectively reduced in systems of coupled nitride quantum dots, leading to an increased spatial overlap of electron and hole wave functions compared to an isolated dot. This finding is in agreement with experimental data reported in the literature and is directly related to the behavior of the built-in potential outside an isolated dot. (C) 2011 American Institute of Physics. (doi:10.1063/1.3665069
Unification of the band anticrossing and cluster-state models of dilute nitride semiconductor alloys
We show that a quantitative description of the conduction band in Ga(In)NAs is obtained by combining the experimentally motivated band anticrossing model with detailed calculations of nitrogen cluster states. The unexpectedly large electron effective mass values observed in many GaNAs samples are due to hybridization between the conduction band edge E- nitrogen cluster states close to the band edge. Similar effects explain the difficulty in observing the higher-lying E+ level at low N composition. We predict a decrease of effective mass with hydrostatic pressure in many GaNAs samples
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