Improved terahertz generation from a photoconductive antenna with metal line arrays
Spiral-pattern photoconductive antennas (PCA) on semi-insulating GaAs substrate were fabricated via UV photolithography and electron beam deposition of Ni/Au layers. Micron-scale Ni/Au metal line arrays were fabricated on the terahertz (THz) emission side of a PCA. The THz emission intensity of the PCA with metal line arrays was measured using THz time-domain spectroscopy, and was compared with that of a reference spiral-pattern PCA having a bare emission side. An enhancement of 6 times in the THz peak-to-peak amplitude (and 42 times in the integrated FFT power) was observed at a fluence of ~1.2 mJ/cm2 and 20 VPP bias voltage. The dependence of the THz signal amplitudes with varying optical pump fluences and emitter bias voltages were investigated to characterize the fabricated PCA's and infer the THz emission mechanism of enhanced THz generation from a PCA integrated with subwavelength metal line arrays.