Nanostructures for Optoelectronics : Device Fabrication and Characterization

Sammanfattning: The nanoscale is an exciting domain when it comes to crystal growth, light-matter interaction and electronics. Especially for optoelectronics, semiconductor nanostructures have many advantages compared to traditional planar structures and are highly interesting for the next generation of solar cells, photodetectors and light emitting diodes. This dissertation explores device fabrication, and electrical and electro-optical characterization of semiconductor nanostructures, with an emphasis on materials and structures suitable for optoelectronics. The first part gives an overview of nanowire synthesis, doping and current challenges in the field. The second part describes doping characterization at the nanoscale using electrical measurement techniques. A fabrication scheme for making nanowire devices for Hall effect characterization and field-effect characterization is presented. Methods for simulating electric transport in nanowires to analyze measurements and determine doping concentration from Hall and field-effect measurements are discussed. Doping incorporation in InP core-shell nanowires is studied with Hall effect and correlated to optical characterization techniques. An experimental comparison between nanowire Hall effect measurements and field-effect measurements is presented. A three-probe device geometry to simplify Hall effect measurements is suggested and experimentally verified. Hall measurements are performed on nanowire-based platelet-structures. The last part of the dissertation describes fabrication and characterization of nanoscale optoelectronic devices. Nanowires with p-n junctions synthesized using the high-throughput and substrate-less Aerotaxy method are characterized and shown to have promising properties. Finally, fabrication and electro-optical characterization of nitride platelet LEDs with emission from UV to red is presented.