InGaN Nanowires on Silicon

In this thesis the growth of InN nanowires on silicon, the alloying of InN nanowires with gallium, and the electrical properties of InN/InGaN-silicon heterostructures for the fabrication of an InGaN/Si tandem solar cell are investigated. InN nanowires fabricated via a spontaneous growth mechanism have a perfect wurtzite structure with a flat top facet. Further measurements show, for example, that the InN nanowires are surrounded by an oxide layer about 5nm thick and have both polarities. Using a nanostructured mask, the position and diameter of the InN nanowires could be controlled. The second focus of the work is on the fabrication of InGaN nanowires. The incorporated Ga content has been determined by various measurement methods. A spatially resolved structural analysis of individual nanowires indicates an inhomogeneous distribution of Ga atoms. All investigated nanowires have an almost pure InN core, which is embedded in a highly Ga-rich InGaN shell. In addition, the electrical properties of the resulting heterostructures are investigated. Samples with different doping types and doping concentrations are analyzed. The current-voltage characteristics of many samples show a rectifying behavior, which strongly depends on the doping of the silicon substrate. The transport processes can be explained by the thermionic emission theory of a Schottky diode. The temperature dependence of the barrier height and the ideality factor of the heterostructures are investigated by current-voltage measurements at temperatures from 200K to 300K. The influence of sample aging and different environmental conditions is also discussed. Band diagrams of corresponding heterostructures are simulated with the software Nextnano++ and are consistent with the experimental data.