487 research outputs found
Impact of alloy disorder on the band structure of compressively strained GaBiAs
The incorporation of bismuth (Bi) in GaAs results in a large reduction of the
band gap energy (E) accompanied with a large increase in the spin-orbit
splitting energy (), leading to the condition that
which is anticipated to reduce so-called CHSH Auger
recombination losses whereby the energy and momentum of a recombining
electron-hole pair is given to a second hole which is excited into the
spin-orbit band. We theoretically investigate the electronic structure of
experimentally grown GaBiAs samples on (100) GaAs substrates by
directly comparing our data with room temperature photo-modulated reflectance
(PR) measurements. Our atomistic theoretical calculations, in agreement with
the PR measurements, confirm that E is equal to for
9. We then theoretically probe the inhomogeneous
broadening of the interband transition energies as a function of the alloy
disorder. The broadening associated with spin-split-off transitions arises from
conventional alloy effects, while the behaviour of the heavy-hole transitions
can be well described using a valence band-anticrossing model. We show that for
the samples containing 8.5% and 10.4% Bi the difficulty in identifying a clear
light-hole-related transition energy from the measured PR data is due to the
significant broadening of the host matrix light-hole states as a result of the
presence of a large number of Bi resonant states in the same energy range and
disorder in the alloy. We further provide quantitative estimates of the impact
of supercell size and the assumed random distribution of Bi atoms on the
interband transition energies in GaBiAs. Our calculations support
a type-I band alignment at the GaBiAs/GaAs interface, consistent
with recent experimental findings
GaAs-based dilute bismide semiconductor lasers:Theory vs. experiment
We present a theoretical analysis of the electronic and optical properties of near-infrared dilute bismide quantum well (QW) lasers grown on GaAs substrates. Our theoretical model is based upon a 12-band k·p Hamiltonian which explicitly incorporates the strong Bi-induced modifications of the band structure in pseudomorphically strained GaBi x As 1-x alloys. We outline the impact of Bi on the gain characteristics of ideal GaBi x As 1-x /(Al)GaAs devices, compare the results of our theoretical calculations to experimental measurements of the spontaneous emission (SE) and optical gain - a first for this emerging material system - and demonstrate quantitative agreement between theory and experiment. Through our theoretical analysis we further demonstrate that this novel class of III-V semiconductor alloys has strong potential for the development of highly efficient GaAs-based semiconductor lasers which promise to deliver uncooled operation at 1.55 μm
Dilute bismide alloys grown on GaAs and InP substrates for improved near- and mid-infrared semiconductor lasers
We present an analysis of dilute bismide quantum well (QW) lasers grown on GaAs and InP substrates. Our theoretical analysis is based upon a 12-band k·p Hamiltonian which directly incorporates the strong impact of Bi incorporation on the band structure using a band-anticrossing approach. For GaBiAs QWs grown on GaAs we analyse the device performance as a function of Bi composition, and quantify the potential to use GaBiAs alloys to realise highly efficient, temperature stable 1.55 μm lasers. We compare our calculations to measured spontaneous emission (SE) and gain spectra for first-generation GaBiAs lasers and demonstrate quantitative agreement between theory and experiment. We also present a theoretical analysis of InGaBiAs alloys grown on InP substrates. We show that this material system is well suited to the development of mid-infrared lasers, and offers the potential to realise highly efficient InP-based diode lasers incorporating type-I QWs and emitting at > 3 μm. We quantify the theoretical performance of this new class of mid-infrared lasers, and identify optimised structures for emission across the application-rich 3 - 5 μm wavelength range. Our results highlight and quantify the potential of dilute bismide alloys to overcome several limitations associated with existing GaAs- and InP-based near- and mid-infrared laser technologies
Genetic and systems level analysis of Drosophila sticky/citron kinase and dFmr1 mutants reveals common regulation of genetic networks
<p>Abstract</p> <p>Background</p> <p>In <it>Drosophila</it>, the genes <it>sticky </it>and <it>dFmr1 </it>have both been shown to regulate cytoskeletal dynamics and chromatin structure. These genes also genetically interact with Argonaute family microRNA regulators. Furthermore, in mammalian systems, both genes have been implicated in neuronal development. Given these genetic and functional similarities, we tested <it>Drosophila sticky </it>and <it>dFmr1 </it>for a genetic interaction and measured whole genome expression in both mutants to assess similarities in gene regulation.</p> <p>Results</p> <p>We found that <it>sticky </it>mutations can dominantly suppress a <it>dFmr1 </it>gain-of-function phenotype in the developing eye, while phenotypes produced by RNAi knock-down of <it>sticky </it>were enhanced by <it>dFmr1 </it>RNAi and a <it>dFmr1 </it>loss-of-function mutation. We also identified a large number of transcripts that were misexpressed in both mutants suggesting that <it>sticky </it>and <it>dFmr1 </it>gene products similarly regulate gene expression. By integrating gene expression data with a protein-protein interaction network, we found that mutations in <it>sticky </it>and <it>dFmr1 </it>resulted in misexpression of common gene networks, and consequently predicted additional specific phenotypes previously not known to be associated with either gene. Further phenotypic analyses validated these predictions.</p> <p>Conclusion</p> <p>These findings establish a functional link between two previously unrelated genes. Microarray analysis indicates that <it>sticky </it>and <it>dFmr1 </it>are both required for regulation of many developmental genes in a variety of cell types. The diversity of transcripts regulated by these two genes suggests a clear cause of the pleiotropy that <it>sticky </it>and <it>dFmr1 </it>mutants display and provides many novel, testable hypotheses about the functions of these genes. As both of these genes are implicated in the development and function of the mammalian brain, these results have relevance to human health as well as to understanding more general biological processes.</p
Theory and design of InGaAsBi mid-infrared semiconductor lasers: type-I quantum wells for emission beyond 3 m on InP substrates
We present a theoretical analysis and optimisation of the properties and
performance of mid-infrared semiconductor lasers based on the dilute bismide
alloy InGaAsBi, grown on conventional (001) InP
substrates. The ability to independently vary the epitaxial strain and emission
wavelength in this quaternary alloy provides significant scope for band
structure engineering. Our calculations demonstrate that structures based on
compressively strained InGaAsBi quantum wells (QWs)
can readily achieve emission wavelengths in the 3 -- 5 m range, and that
these QWs have large type-I band offsets. As such, these structures have the
potential to overcome a number of limitations commonly associated with this
application-rich but technologically challenging wavelength range. By
considering structures having (i) fixed QW thickness and variable strain, and
(ii) fixed strain and variable QW thickness, we quantify key trends in the
properties and performance as functions of the alloy composition, structural
properties, and emission wavelength, and on this basis identify routes towards
the realisation of optimised devices for practical applications. Our analysis
suggests that simple laser structures -- incorporating
InGaAsBi QWs and unstrained ternary
InGaAs barriers -- which are compatible with established
epitaxial growth, provide a route to realising InP-based mid-infrared diode
lasers.Comment: Submitted versio
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