Ultra-high bandwidth (570 GHz) metal-semiconductor-metal traveling-wave-photodetectors

We demonstrate a novel type of ultra-high speed traveling wave photodetector: "metal-semiconductor-metal traveling wave photodetector" (MSM TWPD), and characterized it's ultrahigh electrical bandwidth by E-O sampling technique. The device was fabricated using low-temperature grown GaAs (LTG-GaAs). In order to achieve high internal quantum efficiency, the narrow spacing between electrodes was fabricated by self-aligned process without e-beam lithography. E-O sampling measurement results at different optical pumping level are reported. Ultra-high bandwidth (0.8 ps, 570 GHz transform bandwidth) performance was observed even under high optical power illumination (∼2.2 mW) with 8.1% net quantum efficiency. Compared with LTG-GaAs based p-i-n TWPD and vertically illuminated MSM photodetector (PD), this novel TWPD has higher output saturation current with near THz electrical bandwidth, better quantum efficiency, and can be easily fabricated and integrated with other microwave devices. By utilizing the ultra-high speed performance of this device, we also studied the microwave propagation effect of its generated subpicosecond electrical pulse on integrated CPW line. The measurement results also reveals some microwave behavior of CPW line in near THz frequency regime, which are quit important due to high speed data linking or transmission.