55 research outputs found

    Modeling of the optical gain in ZnO-based quantum cascade lasers

    Get PDF
    ZnO has been proposed recently as a good base material for high-power terahertz quantum cascade lasers (QCLs) operating at room temperature. We have developed a theoretical model for calculation of the optical gain, based on solving the system of rate equations and taking into account relevant scattering mechanisms. This model has been implemented to perform numerical simulations using ZnO/ZnMgO material combination, starting from the conventional design with three well within the active region of the structure. The influence of the layer widths and composition on the output properties has been considered, together with the variation of the number of quantum wells per QCL period.XVIII Young Researchers' Conference Materials Sciences and Engineering : program and the book of abstracts; December 4-6, 2019; Belgrad

    Nonparabolic effects in multiple quantum well structures and influence of external magnetic field on dipole matrix elements

    Get PDF
    We present a method of modeling of nonparabolic effects (NPE) in quantum nanostructures by using second order perturbation theory. We apply this model on multiple quantum well structures and consider the influence of external magnetic field on dipole matrix element which is usually considered constant. The dipole matrix element directly influences the optical gain, and our model can provide a better insight to how NPE and magnetic field influence the gain of quantum nanostructures

    Towards automated design of quantum cascade lasers

    Get PDF
    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

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

    Get PDF
    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

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

    Get PDF
    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

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

    Get PDF
    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

    Electronic structure and electron distribution in an inverse superatom calculated by self-consistent method

    Get PDF
    A full self-consistent procedure, applied to an inverse superatom strucuture is described. It is shown, both numerically and theoretically, that the electron concentration is large, but not maximal, the point of maximum being displaced off centre due to the fact that the second excited level has three times as many electrons as the ground level. Such an effect does not occur in classical quantum wells and superlattices. Moreover it is shown that the self-consistent treatment is necessary for an exact analysis of the energy band structure of the inverse superatom: solving the problem only by a trial rectangular potential gives an error of about 20%

    APPLICABILITY AND QUALITY ASSESSMENT OF THE SET OF EQUIPMENT IN THE PROJECT “POLYGON FOR PHYSICAL ACTIVITY OF SCHOOL-AGED CHILDREN“ IN PRIMARY SCHOOLS WITHOUT GYMNASIA

    Get PDF
    In 2015, 120 main primary schools in Croatia did not have a school gymnasium, and could not carry through the full-time compulsory Physical Education (PE) class. To ensure regular physical exercise to all children and help teachers, the Croatian Institute of Public Health has implemented the project “Polygon for Physical Activity of School-Aged Children”. This paper aims to present the usability and functionality assessment of the multipurpose kinesiology equipment set used in the Project in the primary schools without gymnasia based on the teachers’ experience and appraisals in three independent assessment waves. Results show that after receiving the set the teachers perceived they had better conditions for teaching Physical Education class and managed to fulfil PE curriculum goals and tasks. Students’ motivation for physical education class also improved in some areas, as well as teachers’ satisfaction with the conditions for and school investments in PE class. Most of the teachers perceived that the multipurpose kinesiology equipment set had the potential to improve the quality of PE class and to be used in other classes as well. According to the obtained data it could be assumed that this multipurpose kinesiology equipment set is a positive innovation in the teaching process and presents a strong potential for alleviating the spatial and material problems teachers in schools without gymnasia are experiencing in their work

    Density matrix theory of transport and gain in quantum cascade lasers in a magnetic field

    Get PDF
    A density matrix theory of electron transport and optical gain in quantum cascade lasers in an external magnetic field is formulated. Starting from a general quantum kinetic treatment, we describe the intraperiod and interperiod electron dynamics at the non-Markovian, Markovian, and Boltzmann approximation levels. Interactions of electrons with longitudinal optical phonons and classical light fields are included in the present description. The non-Markovian calculation for a prototype structure reveals a significantly different gain spectra in terms of linewidth and additional polaronic features in comparison to the Markovian and Boltzmann ones. Despite strongly controversial interpretations of the origin of the transport processes in the non- Markovian or Markovian and the Boltzmann approaches, they yield comparable values of the current densities

    Resonantly enhanced bound-continuum intersubband second harmonic generation in optimized asymmetric semiconductor quantum wells

    Get PDF
    A systematic procedure applied to a step-asymmetric quantum well in order to maximize intersubband bound–continuum second-order susceptibility is described. The possibility is explored of obtaining resonantly enhanced nonlinear optical susceptibilities in quantum wells with two bound and a continuum resonance state as the dominant third state. This would significantly extend the range of input radiation photon energies that may be frequency doubled under resonance conditions in realistic structures. Calculation for the AlxGa1−xAs alloy based wells designed for pump photon energies in range of ℏω=200–300 meV indicate a perspective of employing continuum states in resonant second harmonic generation at higher photon energies
    corecore