Multiscale simulations of the electronic structure of III-nitride quantum wells with varied indium content: Connecting atomistic and continuum-based models

Carrier localization effects in III-N heterostructures are often studied in the frame of modified continuum-based models utilizing a single-band effective mass approximation. However, there exists no comparison between the results of a modified continuum model and atomistic calculations on the same underlying disordered energy landscape. We present a theoretical framework that establishes a connection between atomistic tight-binding theory and continuum-based electronic structure models, here a single-band effective mass approximation, and provide such a comparison for the electronic structure of (In,Ga)N quantum wells. In our approach, in principle, the effective masses are the only adjustable parameters since the confinement energy landscape is directly obtained from tight-binding theory. We find that the electronic structure calculated within effective mass approximation and the tight-binding model differ noticeably. However, at least in terms of energy eigenvalues, an improved agreement between the two methods can be achieved by adjusting the band offsets in the continuum model, enabling, therefore, a recipe for constructing a modified continuum model that gives a reasonable approximation of the tight-binding energies. Carrier localization characteristics for energetically low lying, strongly localized states differ, however, significantly from those obtained using the tight-binding model. For energetically higher lying, more delocalized states, good agreement may be achieved. Therefore, the atomistically motivated continuum-based single-band effective mass model established provides a good, computationally efficient alternative to fully atomistic investigations, at least at when targeting questions related to higher temperatures and carrier densities in (In,Ga)N systems

Multiscale simulations of the electronic structure of III-nitride quantum wells with varied indium content: Connecting atomistic and continuum-based models

Carrier localization effects in III-N heterostructures are often studied in the frame of modified continuum-based models utilizing a single-band effective mass approximation. However, there exists no comparison between the results of a modified continuum model and atomistic calculations on the same underlying disordered energy landscape. We present a theoretical framework that establishes a connection between atomistic tight-binding theory and continuum-based electronic structure models, here a single-band effective mass approximation, and provide such a comparison for the electronic structure of (In,Ga)N quantum wells. In our approach, in principle, the effective masses are the only adjustable parameters since the confinement energy landscape is directly obtained from tight-binding theory. We find that the electronic structure calculated within effective mass approximation and the tight-binding model differ noticeably. However, at least in terms of energy eigenvalues, an improved agreement between the two methods can be achieved by adjusting the band offsets in the continuum model, enabling, therefore, a recipe for constructing a modified continuum model that gives a reasonable approximation of the tight-binding energies. Carrier localization characteristics for energetically low lying, strongly localized states differ, however, significantly from those obtained using the tight-binding model. For energetically higher lying, more delocalized states, good agreement may be achieved. Therefore, the atomistically motivated continuum-based single-band effective mass model established provides a good, computationally efficient alternative to fully atomistic investigations, at least at when targeting questions related to higher temperatures and carrier densities in (In,Ga)N systems

Mathematical models as research data via flexiformal theory graphs

Mathematical modeling and simulation (MMS) has now been established as an essential part of the scientific work in many disciplines. It is common to categorize the involved numerical data and to some extent the corresponding scientific software as research data. But both have their origin in mathematical models, therefore any holistic approach to research data in MMS should cover all three aspects: data, software, and models. While the problems of classifying, archiving and making accessible are largely solved for data and first frameworks and systems are emerging for software, the question of how to deal with mathematical models is completely open. In this paper we propose a solution -- to cover all aspects of mathematical models: the underlying mathematical knowledge, the equations, boundary conditions, numeric approximations, and documents in a flexi\-formal framework, which has enough structure to support the various uses of models in scientific and technology workflows. Concretely we propose to use the OMDoc/MMT framework to formalize mathematical models and show the adequacy of this approach by modeling a simple, but non-trivial model: van Roosbroeck's drift-diffusion model for one-dimensional devices. This formalization -- and future extensions -- allows us to support the modeler by e.g. flexibly composing models, visualizing Model Pathway Diagrams, and annotating model equations in documents as induced from the formalized documents by flattening. This directly solves some of the problems in treating MMS as "research data'' and opens the way towards more MKM services for models

Simulation of Static and Dynamic Properties of Edge-Emitting Multi Quantum Well Lasers

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A hybrid quantum-classical modeling approach for electrically driven quantum light sources

The design of electrically driven quantum light sources based on semiconductor quantum dots, such as singlephoton emitters and nanolasers, asks for modeling approaches combining classical device physics with cavity quantum electrodynamics. In particular, one has to connect the well-established fields of semi-classical semiconductor transport theory and the theory of open quantum systems. We present a first step in this direction by coupling the van Roosbroeck system with a Markovian quantum master equation in Lindblad form. The resulting hybrid quantum-classical system obeys the fundamental laws of non-equilibrium thermodynamics and provides a comprehensive description of quantum dot devices on multiple scales: It enables the calculation of quantum optical figures of merit (e.g. the second order intensity correlation function) together with the spatially resolved simulation of the current flow in realistic semiconductor device geometries in a unified way

Simulation of Static and Dynamic Properties of Edge-Emitting Multi Quantum Well Lasers

This paper demonstrates simulation tools for edge-emitting multi quantum well (MQW) lasers. Properties o

Modeling of edge-emitting lasers based ontensile strained Germanium microstrips

In this paper we present a thorough modeling of an edge-emitting laser based on strained germanium microstrips. The full band structure of the tensile strained Germanium (Ge) layer enters the calculation of optical properties. Material gain for strained Ge is used in the two-dimensional simulation of the carrier transport and of the optical field within a cross section of the microstrips orthogonal to the optical cavity. We study optoelectronic properties of the device for two different designs. The simulation results are very promising as they show feasible ways towards Ge emitter devices with lower threshold currents and higher efficiency as published insofar