NUSOD Blog

Connecting Theory and Practice in Optoelectronics

Fundamental limit of quantum device simulations

InGaN_QWThis pictures provides an atomistic view of an InGaN/GaN quantum well [1]. Inside this quantum well (QW), 17% of the Gallium atoms are replaced by Indium atoms which are here randomly distributed (red dots). Such QWs are employed in many modern light-emitting devices, from full-color displays to LED lamps. The emission wavelength is controlled by the Indium concentration.

QW models and device simulations typically ignore this atomistic structure and assume a uniform QW alloy layer with uniform material properties. Such continuum models still deliver reasonable results in many cases. But some phenomena are hard to explain this way and require an atomistic approach. One example is the much discussed efficiency droop that seems to be mainly caused by strong Auger recombination. Recent studies link this effect to the non-uniformity of InGaN quantum wells  (details). Read more of this post

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A handbook by and for the NUSOD community

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Our NUSOD handbook was finally published this month, comprising 1682 pages with 52 chapters written by more than 100 experts from all over the world. I think the handbook format is ideal for beginners but it is also useful for experienced researchers who would like to update and broaden their knowledge in this field.

Mathematical models and simulation methods for optoelectronic devices have experienced a great diversification, mainly driven by the expanding variety of available and envisioned practical applications.  Furthermore, the development of commercial software opens the door for a  rising number of scientists and engineers to perform sophisticated simulation tasks. However, it is often difficult to identify the best approach to a given problem, considering the ever  growing variety and complexity of devices, materials, physical mechanisms, theoretical models, and numerical techniques. Therefore, this handbook offers an introductory yet detailed review of modern optoelectronic device models and simulation techniques. Read more of this post

High-power GaN-based laser with tunnel junction

tunnel junction laserThus far, the highest output power measured on GaN-based lasers is about 7W, as shown in the picture. [1] In comparison, some GaAs-based lasers emit more than 30W in continuous-wave operation at room temperature. A key reason for this difference is the inherently large p-side electrical resistance of GaN-based laser diodes. It leads to strong Joule heating which lowers the gain and boosts various loss mechanisms that eventually cause the typical power roll-off at high currents. [2] Read more of this post

NUSOD 2017 with record attendance

NUSOD-17-sessionA record number of 128 papers was presented last week at the NUSOD 2017 conference,  stimulating many valuable discussions. Summaries of all presentations are now available online. Poster prizes were awarded to papers MP01, MP25, and MP28. The rump session focused on improved publication methods as recently announced on this blog.

I would like to thank all participants and organizers for making this conference a great success and I hope to see many again next year at the 18th NUSOD conference in Hong Kong.

NUSOD 2017 Preview Rump Session: Words cannot express…! Research results are more than just plain text.

Whenever you try to answer a research question by using numerical simulation, you start by developing a (or reusing an already developed) mathematical model. Thereafter, you are developing (or reusing already developed) software to perform your numerical simulation. This produces data that you are now analysing and visualising to interpret the discovered results. Finally, you might want to write it all down in an article and publish it on the arXiv and/or in a scientific journal. In this published form the results consist – apart from a couple of figures or tables – mainly of text. DataNotShownIn most cases mathematical models, software, data, visualisations and so on are not or not fully shown. This makes it difficult for editors, reviewers and readers alike to fully grasp the research and its results, see e.g. How to get your simulation paper accepted. Moreover, it makes it difficult to validate and in many cases impossible to reproduce the results.

In a time when scholarly publication was limited to printed journals and books it was simply not feasible to provide long rows of numbers not to mention interactive 3D figures or a moving series of pictures. However, with the advent of the digital age and its easy accessible and easy to use infrastructures and tools there is no excuse for not publishing the full research story – and that does not only consist of plain text.

Read more of this post