The team from Germany, Poland and China has shown the mechanism responsible for limiting the amount of Indium that can be grown on the indium gallium nitride ((In, Ga)N) thin films that are used for blue LEDs. .
The researchers tried to push the indium content to the limit by growing single atomic layers of InN on GaN. However, independent on growth conditions, indium concentrations have never exceeded 25% – 30% – a clear sign of a fundamentally limiting mechanism. Atomic resolution transmission electron microscopes (TEM) and in-situ reflection high-energy electron diffraction (RHEED) showed that, as soon as the indium content reaches around 25 %, the atoms within the (In, Ga)N monolayer arrange in a regular pattern – single atomic column of In alternates with two atomic columns of Ga atoms (as shown in the scanning electron microscope image above).
“Apparently, a technological bottleneck hampers all the attempts to shift the emission from the green towards the yellow and the red regions of the spectra. Therefore, new original pathways are urgently required to overcome these fundamental limitations,” said Dr. Tobias Schulz, a researcher at the Leibniz-Institut fuer Kristallzuechtung in Berlin, Germany. “For example, growth of InGaN films on high quality InGaN pseudo-substrates that would reduce the strain in the growing layer.”
However, the discovery of ordering may help to overcome well known limitations of the InGaN material system and help improve the optical properties of devices.
The work is a result of a collaboration between Leibniz-Institut fuer Kristallzuechtung (Berlin, Germany), Max-Planck-Institut fuer Eisenforschung (Duesseldorf, Germany), Paul-Drude Institut fuer Festkoerperelektronik (Berlin, Germany), Institute of High-Pressure Physics (Warsaw, Poland), and State Key Laboratory of Artificial Microstructure and Mesoscopic Physics (Beijing, China).
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