Optimizing the metal adhesion layer of plasmonic photoconductive sources for high-power terahertz generation

Plasmonic contact electrodes are very effective for enhancing the radiation power of photoconductive terahertz sources. Au is a preferred metal for plasmonic contact electrodes due to the high plasmonic enhancement factors it offers in the near-infrared regime. However, Au requires an adhesion layer to stick well to photoconductive substrates. We investigate the impact of the Au adhesion layer on the performance of plasmonic photoconductive sources fabricated on GaAs. Our analysis suggests that Cr is the most suitable adhesion layer, offering up to 80% higher radiated terahertz powers than the previously demonstrated plasmonic sources that use Ti as the adhesion layer.