Group-III-nitrides are materials very well suited for a variety of optoelectronic applications as they possess a direct band gap. The band gaps of III-nitride alloys cover an extended wavelength range from the near infrared into the visible and up to the ultra-violet. Additionally, outstanding properties of this material system are "polarization doping" and piezoelectricity. It is possible to obtain two-dimensional carrier densities of about 1013 cm-2 without doping, only due to a discontinuity of the internal polarization at the heterojunction. Thus, electron velocities larger than 2∙107 cm/s have been reached. Nitride transistors have indeed already shown excellent performance in planar structures. Adding up these entire qualities one can conclude that nitrides represent one of the most versatile semiconductor material systems.
However, a persisting problem in the field of group-III nitride epitaxy is the unavailability of native substrates. Although some progress has been achieved for GaN substrates, the vast majority of epitaxial films is still grown on foreign substrates with substantial lattice and thermal mismatch, resulting in a high density of structural defects intersecting the epitaxial layers. Given the high commercial relevance of group-III nitride devices that is predicted to increase further, the investigation of epitaxial growth on novel types of substrates is very important.
At present, our focus is on In-rich (In,Ga)N and InN layers. On that subject we obtained funding by the European Community in an Innovative Training Network supported by the Marie Skłodowska-Curie Actions on a project entitled: Short Period Superlattices for Rational (In,Ga)N