Polarization-entangled mid-infrared photon generation in p-doped semiconductor quantum wells

The optimal design of double quantum well structures for generation of polarization-entangled photons in the mid-infrared range, based on the valence intersubband transitions spontaneous parametric downconversion, is considered. The efficiency and frequency selectivity of the process are also estimated

Symmetry of k·p Hamiltonian in pyramidal InAs/GaAs quantum dots: Application to the calculation of electronic structure

A method for the calculation of the electronic structure of pyramidal self-assembled InAs/GaAs quantum dots is presented. The method is based on exploiting the C-4 symmetry of the 8-band k·p Hamiltonian with the strain taken into account via the continuum mechanical model. The operators representing symmetry group elements were represented in the plane wave basis and the group projectors were used to find the symmetry adapted basis in which the corresponding Hamiltonian matrix is block diagonal with four blocks of approximately equal size. The quantum number of total quasiangular momentum is introduced and the states are classified according to its value. Selection rules for interaction with electromagnetic field in the dipole approximation are derived. The method was applied to calculate electron and hole quasibound states in a periodic array of vertically stacked pyramidal self-assembled InAs/GaAs quantum dots for different values of the distance between the dots and external axial magnetic field. As the distance between the dots in an array is varied, an interesting effect of simultaneous change of ground hole state symmetry, type, and the sign of miniband effective mass is predicted. This effect is explained in terms of the change of biaxial strain. It is also found that the magnetic field splitting of Kramer's double degenerate states is most prominent for the first and second excited state in the conduction band and that the magnetic field can both separate otherwise overlapping minibands and concatenate otherwise nonoverlapping minibands

Optical Methods in Sensing and Imaging for Medical and Biological Applications

The recent advances in optical sources and detectors have opened up new opportunities for sensing and imaging techniques which can be successfully used in biomedical and healthcare applications. This book, entitled ‘Optical Methods in Sensing and Imaging for Medical and Biological Applications’, focuses on various aspects of the research and development related to these areas. The book will be a valuable source of information presenting the recent advances in optical methods and novel techniques, as well as their applications in the fields of biomedicine and healthcare, to anyone interested in this subject

Quantum transport in semiconductor quantum dot superlattices: electron-phonon resonances and polaron effects

Electron transport in periodic quantum dot arrays in the presence of interactions with phonons was investigated using the formalism of nonequilibrium Green's functions. The self-consistent Born approximation was used to model the self-energies. Its validity was checked by comparison with the results obtained by direct diagonalization of the Hamiltonian of interacting electrons and longitudinal optical phonons. The nature of charge transport at electron -- phonon resonances was investigated in detail and contributions from scattering and coherent tunnelling to the current were identified. It was found that at larger values of the structure period the main peak in the current -- field characteristics exhibits a doublet structure which was shown to be a transport signature of polaron effects. At smaller values of the period, electron -- phonon resonances cause multiple peaks in the characteristics. A phenomenological model for treatment of nonuniformities of a realistic quantum dot ensemble was also introduced to estimate the influence of nonuniformities on current -- field characteristics

Towards automated design of quantum cascade lasers

We present an advanced technique for the design and optimization of GaAs/AlGaAs quantum cascade laser structures. It is based on the implementation of the simulated annealing algorithm with the purpose of determining a set of design parameters that satisfy predefined conditions, leading to an enhancement of the device output characteristics. Two important design aspects have been addressed: improved thermal behavior, achieved by the use of higher conduction band offset materials, and a more efficient extraction mechanism, realized via a ladder of three lower laser states, with subsequent pairs separated by the optical phonon energy. A detailed analysis of performance of the obtained structures is carried out within a full self-consistent rate equations model of the carrier dynamics. The latter uses wave functions calculated by the transfer matrix method, and evaluates all relevant carrier–phonon and carrier–carrier scattering rates from each quantized state to all others within the same and neighboring periods of the cascade. These values are then used to form a set of rate equations for the carrier density in each state, enabling further calculation of the current density and gain as a function of the applied field and temperature. This paper addresses the application of the described procedure to the design of lambda~9 µm GaAs-based mid-infrared quantum cascade lasers and presents the output characteristics of some of the designed optimized structures. © 2005 American Institute of Physic

Prospects of temperature performance enhancement through higher resonant phonontransition designs in GaAs-based terahertz quantum-cascade lasers dataset

Data repository that corresponds to figures associated with publication “Prospects of temperature performance enhancement through higher resonant phonon transition designs in GaAs-based terahertz quantum-cascade lasers” and the corresponding Supplementary documen

The self-consistent calculation of discrete and continuous states in spherical semiconductor quantum dots

A self-consistent procedure for calculating the energy structure, wave functions, and charge distribution in spherically symmetric semiconductor quantum dots is presented that takes account of both bound and free-electron states. The Schrödinger and Poisson equations are solved iteratively while using the Morse-type parametrized potential to keep the charge neutrality in each iterative step. Numerical calculations performed for a GaAs-Al0.3Ga0.7As based quantum dot indicate that under realistic doping conditions bound states account for most of the charge accumulated in the dot. However, the self-consistent potential very significantly modifies the free-state wave functions and hence the bound-free transition matrix elements

Dual Resonance Phonon Photon Phonon THz QCL - data.

Dataset that corresponds to work on dual resonant phonon THz QCL. Dataset consists of all figures presented in the paper given as Grace files and simulation data given in Excel files

The self-consistent electronic structure of spherical semiconductor quantum dots including bound and free states

A self-consistent procedure for calculating the energy structure, wave functions and charge distribution in spherically symmetric semiconductor quantum dots is presented, that takes account of both bound and free electron states. The Schrodinger and Poisson equation are solved iteratively while using the Morse-type parametrized potential to keep the charge neutrality in each iterative step. Numerical calculations performed for GaAs-Al0.3Ga0.7As based quantum dot indicate that bound states account for most of the charge accumulated in the dot, while including the free states is necessary only at larger doping levels to describe the depleted region outside the dot

Multiparameter optimization of optical nonlinearities in semiconductor quantum wells by supersymmetric quantum mechanics

The multiparameter procedure of semiconductor quantum well profile optimization, using the supersymmetric quantum mechanics, is described and explored. The method generates families of isospectral potentials that depend on a specified number of scalar parameters, which are then varied so to maximize the desired property of the system, in this case the nonlinear susceptibility χ0(2) which gives rise to the optical rectification. The merits and limits of the multiparameter procedure are discussed