New wide-gap semiconductor materials for opto-electronics and for fundamental research

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The 2014 Physics Nobel prize “for the invention of efficient blue light-emitting diodes (LED) which has enabled bright and energy-saving white light sources” refreshed the interest in wide band-gap materials not only on an academic, but also on a commercial level. With growth techniques and first LEDs developed in the 1970s by Jacques Isaac Pankove, unfortunately compound semiconductor devices based on Galliumnitride (GaN) tended to live in the shadows of their Galliumarsenide-based (GaAs) counterparts. GaN as only one representative of semiconductors with a large band-gap offers the possibility to step into an emerging class of commercial devices exhibiting small emission wavelength and high-breakthrough voltage, but also allows to probe an previously unexplored regime of mesoscopic physics due to different intrinsic material properties compared to the traditional systems GaAs or Silicon (Si). As a consequence of enhanced electron-electron interactions in wide band-gap systems, deviation from the single electron picture towards the formation of quasi-particles is expected. Unfortunately the growth of wide band-gap material has not reached the maturity as GaAs or Si. While GaN thin films are synthesized with almost identical growth techniques like GaAs, the fabrication of e.g. high-mobility 2-dimensional electron gases (2DEGs) is impeded by substrate quality and availibilty. Our effort on launching a cost- and labor-intense campaign to growth ultra-pure GaN/AlGaN heterostructures on the highest-quality substrates accessible aims at the ultimate goal to demonstrate electron mobilities exceeding reported values, novel electronic and optoelectronic device concepts as well as the exploration of previously inaccessible terrains in mesoscopia. Our ideas imply comparative studies of GaN/AlGaN, ZnO/MgZnO and GaAs/AlGaAs heterostructures with similar parameters under identical experimental conditions. For example, we plan to investigate electron plasma properties in wide band-gap systems and to develop fast detectors and modulators for microwave radiation. Prototypes of high-speed wireless communication devices operating at 100-200 GHz carrier frequency ensuring information rates up to 50 Gbit/s will be a practical consequence. In addition the investigation of correlation and fermi-liquid effects in these novel 2D electron systems with strong interaction and heavy mass enables a new view on many-particle physics, namely the fractional quantum Hall effect. The knowledge gained in the course of the project could become a basis for the development of a new class of miniature semiconductor elements for classical and quantum electronics.