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16 July 2008


PolarCoN project awarded €2m to close ‘green gap’

The German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) and the Swiss National Science Foundation (SNF) have awarded funding of about €2m for the first phase (from 2008 to 2011) of the new transregional research unit ‘PolarCoN’, involving a consortium of eight research groups.

The consortium aims to control the polarization effects in group III nitride-based heterostructures and investigate various approaches towards their application in commercial optoelectronic devices. The challenge is to close the so-called ‘green gap’ describing the lower efficiency in GaN-based light emitters operating at green wavelengths compared to blue and ultraviolet wavelengths and, ultimately, to develop green -emitting nitride-based laser diodes. One obstacle is the polar character of GaN and related compounds, in particular for devices grown along the crystalline c-axis.

Under project coordinator Ferdinand Scholz of Ulm University’s Institute of Optoelectronics, the PolarCoN team will investigate possibilities of closing the green gap by studying non-polar nitride-based heterostructures and devices.

The main approach will be the epitaxial growth of such structures in non-polar or semi-polar directions, which requires new strategies to overcome a number of material and structural problems.

The group will work on epitaxial growth of defect-free non-polar materials including the development of free-standing non-polar and semi-polar GaN substrates. On such templates, optoelectronic device structures will be grown, with a major focus on longer-wavelength, non-polar laser diodes. The respective building blocks – active quantum wells, n- and p-type doping, device processing, mirror fabrication etc – will be developed by the different groups of the consortium and supported by theoretical modelling efforts.

Another approach will be the minimization of any polarization-induced fields on c-plane surfaces by polarization-matching material combinations such as AlInN-GaInN.

The eight research organizations forming the PolarCoN consortium are Ulm University’s Institute of Optoelectronics (as co-ordinator), Technische Universität Berlin’s Institute of Solid State Physics, Technische Universität Braunschweig’s Institute of Applied Physics, ETH Zürich’s Integrated Systems Laboratory, Otto-von-Guericke University Magdeburg’s Institute of Experimental Physics, the University Regensburg’s Institute of Experimental and Applied Physics, and Universität Stuttgart’s Institut für Halbleiteroptik und Funktionelle Grenzflächen.

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