Effects of Crystallographic Orientation of GaAs Substrate and the Period of Plasmon Grid on THz Antenna Performance.

An alternative approach is proposed to improve the conventional (based on the low‐temperature grown GaAs and Si‐doped GaAs superlattice) photoconductive antenna (PCA) performance by modification of the planar electrodes design and crystallographic orientations of the GaAs substrate ((100) and (111)‐A). The electrode scheme design includes a combination of logarithmic spiral, bow‐tie, and plasmonic antennas and results in appearance of sharp resonant peaks, high spectral bandwidth and high signal‐to‐noise ratio, and significant enhancement of the output terahertz (THz) power. The material design leads to significant increase in the THz output power (by 6.4 in GaAs (100), by 5.6 in GaAs (111)‐A PCAs) regarding to a conventional antenna. The substrate crystallographic cut direction influences the relaxation time constant of photoexcited charge carriers being an order of magnitude smaller in the sample grown on the GaAs (111)‐A than in the one on the GaAs (100). The simulation model supports experimental results demonstrating that the optimal period of the plasmonic antenna grid providing the highest efficiency of THz radiation generation, is about 200 nm. Comparison of the THz spectra in manufactured antennas against the conventional stripline PCA shows a broadening band toward the low‐frequency region down to 0.1 THz with a resonance at 0.2 THz. [ABSTRACT FROM AUTHOR]