The successor to the light bulb

FAU academics research the formation of nitrides

Traditional light bulbs are being phased out and replaced with energy-saving bulbs. However, researchers have for some time been working to develop new, very bright and simultaneously far more energy-efficient light diodes. To do so, they are using nitrides: special crystals grown via ammonothermal synthesis. Researchers at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Ludwig-Maximilians-Universität München and Universität Stuttgart intend to research this process in greater detail. The German Research Council (DFG) is now set to support the project “The chemistry and technology behind the ammonothermal synthesis of nitrides” for the next three years with around €2.7 million.

Distributed across seven sub-projects, the research teams want to build up a basic body of knowledge on ammonothermal synthesis. Their objective is to understand and influence the processes that take place during synthesis, in order to establish scientific findings for the targeted farming of high quality nitrides. The results are intended to form the basis for the development of new materials based on nitride semiconductors, which could then be used, for example, in light diodes or lasers, and in many other areas, such as semiconductor electronics.

In addition to the project’s spokesperson, Prof. Dr. Eberhard Schlücker (director of the Department for Process Mechanics and Systems Engineering), the following FAU staff are involved: Prof. Dr. Wilhelm Schwieger (Department for Chemical Reaction Engineering), Prof. Dr. Peter Wellmann (Department for Material Sciences [Electronics and Power Engineering]), Prof. Dr. Lothar Frey (Director of the Department for Electronic Components) and Dr. Elke Meißner (Fraunhofer IISB).

Ammonothermal synthesis

“As an example, gallium nitride is used in modern light diodes, LEDS”, explains Prof. Schlücker. “The gallium nitride crystallises as a layer on sapphire substrate, for example, creating a low-energy, bright light.” However, this method has the disadvantage that tensions appear in the components as a result of the different physical characteristics of the crystals and the substrates. This causes a large number of crystal production faults (shifting), poor durability and often unsatisfactory material quality. The solution to these problems is monocrystals, i.e. crystals that do not grow on other substrates, but rather on small pieces of crystal composed of the same material. One of the most promising methods of producing such monocrystal nitrides is ammonothermal synthesis: these crystals can be created in an ammoniac atmosphere under very high pressure of 3,000 bars and at 600 degrees Celsius in gas-tight, sealable pressure tanks. “But we still do not know what individual reactions take place, exactly why crystals grow, what materials play a supporting role and how substance transport takes place,” says Schlücker. Because of the extreme reaction conditions, researchers have never been able to measures the processes that take place during the reaction.

Erlangen scientists’ research project

The individual sub-projects aim to research different aspects of ammonothermal synthesis. This should lead to the production of highly purified gallium nitride, which could form the basis for the production of energy-efficient light diodes. Furthermore, the research team aims to develop new measuring procedures to precisely analyse all aspects of synthesis. To this end, Prof. Schlücker and the project’s coordinator, Dr. Nicolas Alt, have, with others, developed a “visible cell”. This cell makes it possible, for the first time, to record the flow conditions and reaction processes which are taking place at high pressure and temperatures in the pressure tanks, using high speed cameras and laser spectroscopy measuring techniques. This should allow crystallisation processes to be optimised and new sorts of nitride developed. The team also intend to produce improved equipment for nitride farming.

More information is available online at www.ammono-for.de.

Further information for the press:

uni | media service | research No. 46/2011 on 27.9.2011