This dissertation presents new types of terahertz photomixers based on nanoelectrodes which significantly enhance the terahertz output power and the operation frequency. 1-D (silver nanowire) and 2-D (multi-layer graphene) nanomaterials are essential inventions supporting the new design. The new design is placed emphasis on a reduction of the photomixer capacitance and on an improved device reliability.
This work deals with two different types of terahertz photomixers, namely lateral and vertical configurations. Both silver nanowire and multi-layer graphene have been used in the lateral photomixer fabrication, whereas the fabrication of the vertical photomixer has been performed using only silver nanowire. The 1-D photomixer of both configurations produced a large reduction of the capacitance of around one order of magnitude as compared to conventional photomixers. The DC characteristics of all types of the nanoelectrode photomixers showed a large increase of the photocurrent of up to 20 and 32 times in lateral and vertical photomixers, respectively, as compared to the photocurrent in the conventional photomixer. The terahertz measurement results of the 1-D lateral photomixer clearly showed the effect of low capacitance and high photocurrent by higher terahertz power radiation and wider frequency range as compared to conventional photomixers. For the graphene photomixer, the results prove the photocurrent enhancement in the terahertz output with increased device reliability due to the graphene involvement.
In this dissertation all respective fabrication, characterization, and measurement details are presented and descripted. The results show the great potential for terahertz applications like spectroscopy and imaging systems.