Electrical transport in GaN and InN nanowires

This thesis discusses the analysis of the electrical transport in GaN and InN nanowires at room temperature and deep temperatures. From those measurements two different transport models for those two in matter of the band banding completely different materials have been found. In the investigation of the GaN nanowires the main focus was the electrical transport in dependence of the diameter and the n-doping. With the use of IV-measurements on those MBE grown nanowires with different diameters at dark and under UV illumination as well as the decay of the persistent photocurrent, it was possible to find an for GaN untypical behaviour. The electrical transport in those wires is extremely diameter dependent. The dark current shows space charged limited current. With the help of those cognitions a diameter dependent transport model could be found. The transport phenomena in those wires is based on the diameter depending band bending at the edge of the wires caused by the Fermi level pinning inside the forbidden band. This model can be fit to the data with the three parameter doping, fermi level pinning and wire diameter. On the base of those effects a method to determine the doping concentration inside those wires without field effect measurements and contact resistance has been developed. The defect structure inside those wires has been analysed with the help of spectral photoluminescence measurements. Here several defect bands have been found and it was possible with help of several contacts on one single wire to determine different defect regions along the wire and to explain them by the lattice mismatch between nanowire and substrate. Further temperature depending measurements and investigations on Schottky contacted wires as well as on GaN wires with AlN tunnel structures complete the work on GaN. The electrical characterisation on a large scale of undoped and doped InN nanowires shows linear growth of the dark current with the diameter up to wires of around 100 nm. Furthermore that III-V semiconductor shows metallic behaviour on temperature dependent investigations. From these results it can be concluded, that the transport occurs mainly on the edge of the nanowire, where due to the downwards Fermi level pinning an electron accumulation zone is exists. To investigate the transport behaviours of those InN nanowires well directed magneto transport measurements have been performed at deep temperatures 0.3 K and 30 K. With a perpendicular magnetic field universal current fluctuations could be found and the phase coherence length could be extracted from those data. Measurements with an axial magnetic field showed a periodic oscillation pattern with the period of φ. These periodic oscillation can be lead to coherent Eigenstates inside the 2DEG on the wires edges. (orig.)