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- Vision
- Figure 4.4 Integration challenges and cluster vision for the theory and modelling work-package
Qualitative | ||
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Integration within
cluster |
Day-to-day co-operation, exchange of samples, sharing know-how, etc Level of formal links between partners, e.g. studentships, researchers Contracts, grants and formal training activities involving more than 1 cluster partner
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Increase in number of joint publications Total number of visits between partners Number of “major” challenges addressed through meetings, and progress made
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Integration across
clusters |
Increase in availability of inputs on growth, material characterisation and theory/modelling Increase in device researchers with cross-disciplinary skills through cross-cluster training Level of involvement of non-cluster partners in technical meetings
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Number of cross-cluster visits Degree of activity across clusters for input data generation and feedback Number of publications with at least 1 partner from another cluster |
WP4: Theory and Modelling
The targets for this work-package are to develop enhanced theoretical understanding of the optical and electrical properties of dilute nitride materials in bulk form, and in quantum well (QW) and quantum dots (QD), and also to develop simulation and modelling tools with predictive capability for the behaviour of optical, optoelectronic and electronic devices fabricated in the dilute nitrides material system. The range of materials to be considered will include, but not necessarily be limited to, those studied in the complementary work-packages on growth and material characterisation. Similarly, the devices to be modelled will be those addressed by the work-package concerned with devices and device integration.
To date, most theoretical attention has been focussed on understanding the band structure of the GaInAsN/GaAs system and on evaluating gain spectra and threshold conditions for 1.3 m lasers. However, within the DiNAMITe consortium we will broaden the range of materials and devices to be studied. As we increase our understanding of band structure and the effects of strain, defects, etc in the dilute nitrides we can calculate the electrical and optical properties, including radiative and non-radiative recombination for the materials and structures of interest. The key integration challenges and cluster vision for the devices work-package are illustrated in Fig. 4.4. A primary challenge will be to select only the most pertinent aspects of fundamental theory in formulating device models; these must be rigorously calibrated against inputs from the growth and characterisation clusters
Our simulation approaches are mostly composed of mutually interrelated parts describing optical, electrical, gain, thermal, and sometimes mechanical phenomena occurring in optoelectronics devices under pulsed or continuous-wave operation. These physical phenomena are, however, strongly and mutually interrelated. Hence our comprehensive models of various optoelectronics devices contain not only a detailed description of particular physical processes crucial to their operation but they also require accurate self-consistent parts including numerous interactions between various individual physical phenomena. The above models enable us to better understand the physics of operation of devices in the whole complexity of a dense network of many nonlinear and mutual interactions between individual physical processes.
In constructing simulation tools, the appropriate optical and electrical properties must be accurately modelled and again tested against data from other clusters. Cross-cluster exchanges and training will be very important in ensuring that the appropriate inputs are selected and used with caution. Significant effects of nonlinearity, coupling and feedback must be included if the models are to be of real value. The vision is for the theory not only to indicate the trends of device behaviour with various parameters, but also to have a predictive capability in guiding device design and optimisation.
Vision
>Predictive capability
> Parameter trends
> Design rules
> Device design
> Device optimisation
Coupling
Nonlinearity
Adapt suitable properties
for specific devices
Select key
fundamental
inputs &
omit others
EELs, VCSELs SESAMS QWIPs
SOAs VCSOAs modulators RCEPDs
Optical properties
Electrical transport
Rad. & non-rad. recombination
Feedback
Band structures Strain Defects
Figure 4.4 Integration challenges and cluster vision for the theory and modelling work-package
From the theoretical point of view the main research tasks may be grouped into calculations of fundamental electronic properties, optical and electrical transport properties, and radiative and non-radiative recombination mechanisms. Under the first heading we include the topics of band formation and band structure, with an especial focus on assessing the accuracy of the band anticrossing (BAC) model that is widely used for GaInAsN. This will lead to a study of the effects of N and In compositions and hence to design rules for achieving emission/absorption at specific wavelengths. Calculations of densities-of-states and of effective mass values for electrons and holes will be made and then importance of conduction band non-parabolicity will be assessed for the various materials of interest. The important effects of strain in epilayers, QWs and QDs must be included in the theoretical studies, and issues of band alignment in heterostructures will be addressed. Fortunately the DiNAMITe consortium membership is well provided with expertise in all these topics and many of the partners have already made very significant contributions to the field (see Table of core skills below). Specialised theoretical topics also feature in the plans of the consortium members, and these include envelop function calculations of excitonic properties, multiplet N states in dilute nitrides, properties induced by short range order effects, the effects of potential fluctuation and the role of hydrogen on band structure.
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Institute |
Core Skill |
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Bilkent |
Many body effects, modelling of devices, scattering mechanisms, electron-phonon effects |
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Bristol |
Materials and gain modelling, small and large signal modulation, dynamical laser modelling |
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INSA |
Band structure engineering of InGaAsN structures (barrier GaAs, GaAsN, GaAsP, InGaAsP/InP) |
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Dokuz Eylul |
Band structure, Stark effect, intense field effect, density of state calculations, exchange correlation effect on subband population and mobility calculations. |
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Essex |
Theory of band structures, gain and optical properties, device design, novel device concepts and modelling |
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Lodz |
Simulation of optoelectronic devices |
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NMRC |
Calculation of electronic structure and gain characteristics of dilute nitride media |
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Philipps Marburg |
Band structure, carrier relaxation, optical properties |
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Surrey |
Modelling of material and lasers based upon dilute nitrides |
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