84 research outputs found
Electromagnetic modelling of a monolithic pulse reshaper based on a photonic crystal waveguide integrated with a SOA
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
Modelling spin relaxation in semiconductor quantum wells: modifying the Elliot process
A model of the Elliot process for spin relaxation is developed that explicitly incorporates the Dresselhaus spin-splitting of the conduction band in semiconductors lacking an inversion symmetry. It is found that this model reduces to existing models in bulk if the scattering matrices are constructed from a superposition of eigenstates. It is shown that the amplitude for intra-subband spin relaxation disappears in quantum wells on the basis of existing models. However, an amplitude due to the Dresselhaus spin-splitting remains, becoming increasingly important as the well becomes narrower. It is also shown that this component does not disappear for scattering between spin states at the same wavevector. It is concluded that for quantum wells and lower dimensional semiconductors that this modified model should be used in analysis of the spin dynamics
Combination schemes for turning point prediction
We propose new forecast combination schemes for predicting turning points of business cycles. The combination schemes deal with the forecasting performance of a given set of models and possibly providing better turning point predictions. We consider turning point predictions generated by autoregressive (AR) and Markov-Switching AR models, which are commonly used for business cycle analysis. In order to account for parameter uncertainty we consider a Bayesian approach to both estimation and prediction and compare, in terms of statistical accuracy, the individual models and the combined turning point predictions for the United States and Euro area business cycles
Absorption spectra of dipolar Frenkel excitons in two-dimensional lattices with configurational disorder: Long-range interaction and motional narrowing effects
PHOSPHATE ABSORPTION BY PLANTS FROM HABITATS OF DIFFERENT PHOSPHATE STATUS. II ABSORPTION AND INCORPORATION OF PHOSPHATE BY INTACT PLANTS
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