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

We demonstrate an ultra-high speed metal-semiconductor-metal traveling wave photodetector (MSM TWPD), and characterize its ultra-high electrical bandwidth by an 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 a 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 TWPDs and vertically illuminated MSM photodetectors (PD), this novel TWTD 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 an integrated CPW line