Public Physic Colloquium in the Summer Terms 2010 in Münster
Place:     Germany, 48149 Münster, Wilhelm-Klemm-Str. 10, IG I, HS 2
Time:     Thursday, 06.05.2010  16:00 h c.t.
Colloquium Coffee at 15:45 h  at the Lecture Hall

Self assembled GaN nanostructures: physics and application
Prof. Dr. Martin Eickhoff, I.Physikalisches Institut, Justus-Liebig-Universität Gießen

Due to the low density of structural defects and the absence of strain, group III-nitride nanowires are an ideal model system for the analysis of basic material properties. In addition, nanowire heterostructures present a promising approach for the realization of improved optoelectronic or nanoelectronic devices.
We report on catalyst-free nucleation and growth of undoped, Si- (n-type) and Mg- (p-type) doped GaN nanowires by plasma assisted molecular beam epitaxy and demonstrate the growth of GaN and InGaN nanodisc (ND) structures realized by fabrication of axial heterostructures within nanowires with a diameter of 30 nm. The optical properties and carrier confinement in AlGaN/GaN nanowire heterostructures on Si(111) substrates will be analyzed. Photoluminescence measurements showed an increase of the emission energy with increasing Al content up to Al concentrations of approximately 40%, indicating the dominant influence of confinement effects in this regime. For higher Al concentrations, the emission energy decreases due to the increasing influence of the polarization-induced quantum confined Stark effect. The influence of the Al content in the barriers and the structural properties of the heterostructures on the electric fields in the NDs, the thermal stability of the photoluminescence, and the emission broadening will be discussed.
We demonstrate the application of such structures in optochemical transducers for the detection of hydrogen. Here, the luminescence characteristics of GaN nanodiscs in Pt-coated nanowires are altered in the presence of molecular hydrogen. At a temperature of 350°C the detection limit is below 10 ppm.