Nanowires (NWs) have enormous potential for a number of future applications, especially in the field of optoelectronics. This thesis advances key areas in optoelectronic nanowire device fabrication. The studied key areas focus on the reduction of fabrication costs and on improving the performance of complete devices, both of which are essential for practical applications. Ordinary window glass is showed to be a feasible growth platform for GaAs NWs, which additionally produces high crystalline and optical quality NWs. These improvements are attributed to impurities originating from the glass. Another low-cost pathway for NW production studied here was Al-doped ZnO buffer layers, which are transparent and conductive. These layers could be deposited on nearly any substrate, and NWs could be subsequently grown on top irrespective of the underlying material.Surface states are detrimental especially for GaAs NW device performance, for which different passivation methods are presented. Widely used AlGaAs shells are shown to alter the optical processes in the NWs, and Al segregation is shown to occur in the shell. Also a novel passivation method is presented using ultrathin InP or GaP capping layers, which provides strong passivation while causing minimal side-effects. Novel fabrication method is presented for large-area position-controlled NW growth. This method utilizes laser interference lithography that is fast and can be performed with relatively simple equipment. In addition, fabrication of dualtype NWs on a single substrate is presented. This method exploits two different NW growth modes and allows the growth of dissimilar NWs side-by-side. The dualtype NWs can enhance light trapping in solar cells and photodetectors, or expand the emitted wavelength range in light-emitting diodes. Another critical step in NW device fabrication is the contact isolation. This work presents a facile and lithography-free method to create shell-substrate isolated core-shell nanowires via spin-on-glass deposition and NW regrowth techniques. The method allows easier production of core-shell NW devices e.g. when NWs are grown directly on electrodes. NW isolation was additionally performed via encapsulation with parylene-C. This process provides antireflection coating for the NWs as well as electrical isolation for electrical contacts, and is suitable for various situations where current isolation methods are suboptimal.
|Publication status||Published - 2016|
|MoE publication type||G5 Doctoral dissertation (article)|
- nanowire, GaAs, vapor-liquid-solid, MOVPE, photoluminescence, passivation, reflectance, planarization