Photonic Terahertz-Wave Generation Using Slot-Antenna-Integrated Uni-Traveling-Carrier Photodiodes

Widely frequency-tunable terahertz-wave generation with enhanced output power was investigated using slot-antenna-integrated uni-traveling-carrier photodiodes (UTC-PDs). Based on numerical analysis, the optimum antenna configuration for simultaneously attaining increased output power and relatively broad bandwidth was determined. Slot-antenna-integrated UTC-PDs (short- and long-slot) and a broadband bowtie-antenna-integrated UTC-PD were fabricated and analyzed by comparing their characteristics. The slot-antenna-integrated UTC-PDs exhibited two to three times larger output power at their resonant peak frequencies than that of the bowtie-antenna-integrated UTC-PD. Output-power enhancement was attained at frequencies from 900 GHz to 1.6 THz for the short-slot device and from 350 to 850 GHz for the long-slot device, and these characteristics were in good agreement with the numerical analysis. The typical output power obtained was 3.5 μW for the short-slot device at 1.25 THz and 28 μW for the long-slot device at 700 GHz both for a photocurrent of 10 mA with a bias voltage of -0.4 V.