FOR 957:  Polarisation Field Control in Nitride Light Emitters

• Subject Area: Physics
• Term: from 2008 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 48042628

The Research Unit PolarCoN aims to control polarisation effects in group III nitride-based heterostructures and investigate various approaches towards application in optoelectronic devices.
The challenge is to close the so-called "green gap" describing lower efficiency in GaN based green light emitters as opposed to their blue and ultraviolet counterparts and, ultimately, to develop green nitride-based laser diodes. One of the obstacles is thought to be the polar character of GaN and related compounds when grown along the conventional crystalline c-axis. This leads to strong internal electric fields as a consequence of the spontaneous and piezoelectric polarisations in strained GaInN quantum wells acting as active layers in most nitride-based light emitting devices.
These fields are responsible for a local separation of electrons and holes in the active quantum wells thus significantly reducing their radiative recombination probability.
The PolarCoN team will investigate possibilities to close 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- or semipolar directions, which requires new strategies to overcome a number of material and structural problems. Another approach is the minimisation of any polarisation induced fields on c-plane surfaces by polarisation matching material combinations like AlInN-GaInN. The Research Unit will work on epitaxial growth of defect-free nonpolar materials including the development of free-standing non- and semipolar GaN substrates by hydride vapour phase epitaxy. On such templates, optoelectronic device structures will be grown by metalorganic vapour phase epitaxy with a major focus on longer wavelength, nonpolar 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 eventually leading to carefully adjusted joint experiments. A support by sophisticated characterisation and theoretical modelling efforts will further help to reach our ambitious goals.
Partner organisations are: Institute of Optoelectronics, Ulm University - Coordinator; Institute of Solid State Physics, TU Berlin; Institute of Applied Physics, TU Braunschweig; Institute of Experimental Physics, Otto-von-Guericke University Magdeburg; Institute of Experimental and Applied Physics, University Regensburg; Institut für Halbleiteroptik und Funktionelle Grenzflächen, University Stuttgart; Integrated Systems Laboratory, ETH Zürich.

• DFG Programme: Research Units

Projects

• Advanced Electro-Optical Modeling of III-Nitride Light Emitters (Applicant Witzigmann, Bernd )
• coordination project (Applicant Scholz, Ferdinand )
• High In-containing long wavelength GaInN nanostructures on semi-polar surfaces (Applicant Jetter, Michael )
• High-Indium-content nonpolar quantum wells for green, yellow, and red light emitters (Applicant Hangleiter, Andreas )
• Investigations on HVPE - grown InGaN quantum wells on non- and semipolar GaN (Applicant Zweck, Josef )
• Investigations on HVPE of non-and semipolar GaN (Applicant Scholz, Ferdinand )
• Micro-photoluminescence analysis of semi- and non-polar nitrides: local efficiency and transport (Applicant Schwarz, Ulrich Theodor )
• Microscopic Correlation of Electronic and Optical Properties with the Crystalline Real Structure of Polarization Field Controlled Group-III-Nitrides (Applicant Bertram, Frank )
• Polarization field control in GaInN quantum well heterostructures on semipolar growth surfaces (Applicant Kneissl, Michael )
• Polarization reduced GaN layers for light emitters on planar silicon substrates (Applicant Dadgar, Armin )
• Semipolar GaInN quantum wells on pre-structured surfaces for applications in laser diodes (Applicant Scholz, Ferdinand )

• Spokesperson: Professor Dr. Ferdinand Scholz