We are a research group at i-MEET, University of Erlangen, investigating growth and characterization of bulk single crystals of aluminium nitride (AlN) and related materials. These crystals, cut into substrates, provide excellent properties for novel devices in UV optoelectronics (deep-UV LEDs, lasers and detectors) and GHz communication. As an example, the advent of UV-LEDs will facilitate the energy-efficient disinfection of water and air at point-of-use (e.g. attached directly on any water tap) due to their compact size and low voltage operation.
Bulk AlN crystals are most successfully grown by a sublimation-recondensation process (PVT growth) at temperatures exceeding 2000°C. This method derives from the fact that every solid or liquid has a tendency to evaporate into a gaseous form before its melting or decomposition point. Gaseous molecules move to the coldest spot of a compartment and condense back to their liquid or solid form (comparable with a steamy mirror after a shower). We operate several growth facilities and are able to produce crystals with up to 2 inch in diameter. The preparation and analysis capabilities at i-MEET are used to investigate the crystals’ optical, electrical and structural properties in order to further advance growth technology. Concurrently, the group has launched a spin-off, CrystAl-N GmbH., to commercialize AlN substrates. The company is working closely with university and still has some of its laboratories located on the campus.
The group is headed by Priv.-Doz. Dr. Matthias Bickermann.
The images show an AlN bulk crystal, a PVT growth reactor, and sample AlN substrates (from left to right). In the upper right, a schematic of the growth set-up is presented, showing the AlN source material (yellow) and the seed (green) in a container with heat insulation and coils for inducing Joule’s heat into the container.