Wide bandgap semiconductor research
Research Fields
Our group has been active in the
field of wide bandgap semiconductors, especially Gallium Nitride
(GaN)since about 1994. The main research directions are
Other areas of research are
Various tools are employed for
the
characterization of electrical, optical,
and structural properties of GaN materials and devices. We worked on various
sponsored projects and produced several
publications.
Background
Gallium nitride (GaN) is a III-V
semiconductor with a direct bandgap of about 3.4 eV. The material
can be alloyed with InN and AlN, allowing for bandgap energies
anywhere between 1.9 eV and 6.2 eV, and for the fabrication
of heterostructures. Large interest in this materials system
arises from the fact that efficient light emission at short
wavelengths (green, blue, UV) can in principle be realized.
Unfortunately there is no feasible bulk growth technique for
nitride semiconductors. Therefore, the material is grown epitaxially
on a substrate with poorly matched lattice constants and thermal
expansion coefficients. The resulting low material quality,
especially the high dislocation count, had initially discouraged
any further work. However, persistent efforts to improve the
growth procedure, noteworthy by Shuji Nakamura, have allowed
the Japanese company Nichia to produce highly efficient green,
blue, and UV light-emitting diodes (LED) as well as blue and
ultraviolet laser diodes (LD). Today, Nitride-based devices
are expected to generate large revenues in areas like DVD and
laser printing (LD), microwave power applications (high electron
mobility transistors, HEMT), and solid-state lighting including
white-light generation (LED).
