The Precise Lighting

The color of an LED can be adjusted, among other things, by the size of its semiconductor crystals. A researcher from Munich and Linz shows how the nanometer is exactly inexpensive and suitable for industrial use.

Unlike the good old light bulb, light emitting diodes (LEDs) radiate in defined colors from infrared to ultraviolet. The exact wavelength depends on the type of semiconductor material, the core of the LEDs. For some materials, the color can also be adjusted by the size of the semiconductor crystals. If this is in the range of a few nanometers, quantum effects are applied.

Scientists from the LMU have now developed a method with their colleagues from the University of Linz to produce semi-crystalline nanocrystals of a defined size from the cheap mineral oxide perovskite. The crystals are very stable, so that the LEDs have a high color fidelity - an important quality feature. In addition, the semiconductor can be used in printing processes, for example in the production of LEDs for displays.

Decisive for the method of the scientists is a few nanometer thin layer with waffel-like structure. The wells are reminiscent of tiny "reaction pots" and their shape and volume determine the final size of the growing nanocrystals. "We were able to determine the crystal size best with high-energy X-ray radiation at the German Electron Synchrotron in Hamburg", reports the LMU researcher Dr. Bert Nickel from the Cluster of Excellence "Nanosystems Initiative Munich" (NIM).

The thin films are produced by an inexpensive electrochemical process and are practically a direct component of the later LEDs. "Our nanostructured oxide layers have the additional effect of protecting the semiconductor crystals from environmental influences such as oxygen and water, thus increasing the lifetime," explains Dr. Martin Kaltenbrunner from the University of Linz. "As a next step, we will try to further increase the efficiency of the diodes and develop new application areas, such as in flexible displays."