Enhancing the Source-Side Transient Response of Logarithmic Double-Spiral Terahertz Photoconductive Antennas Using a...

The smooth central feed boundary of a logarithmic double-spiral terahertz photoconductive antenna can limit the spatial overlap between the high-field region and photogenerated carriers, thereby restricting the source-side transient response. We introduced a micrometer-scale tip array along the central feed boundary and investigated the influence of tip apex angle, height, and spacing through a transient semiconductor model in COMSOL Multiphysics. The photocurrent derivative, which is proportional to the emitted terahertz electric field under the transient-current approximation, was adopted as the source-side response metric. The tip array enhanced the response by redistributing the local bias field and bringing the carrier-collection boundary closer to the illuminated region. Within the investigated ranges, tip height produced the strongest response variation, whereas the influence of the apex angle remained limited over 10-50°, and further reducing d from 0.5 to 0.25 μm resulted in only a marginal response improvement. For θ = 30°, h = 1.0 μm, and d = 0.5 μm, the positive-peak and peak-to-peak enhancement ratios reached 100.1% and 103.9%, respectively. These results provide source-side design guidance for parameter selection while qualitatively considering geometric perturbation and fabrication practicality.