Ultrahigh bandwidth MSM traveling-wave photodetectors

Summary form only given. In this paper we demonstrate a new type of ultra-high speed photodetector: MSM TWPD. By utilizing LTG-GaAs as the absorption layer, this device structure provides quasi-TEM microwave mode with a velocity close to, or even higher than the optical velocity with-an extremely wide velocity matched bandwidth. MSM TWPD structure has a better bandwidth performance than p-i-n TWPD owing to its lower microwave loss, higher microwave velocity, and better impedance matching between the electrical transmission line of TWPDs and external electric load. With a preliminary device fabrication using self-aligned structures, the measured impulse response exhibits 0.8 ps pulsewidth with a corresponding 3 dB bandwidth over 570 GHz even under high power excitation. Even wider bandwidth performance was obtained for low power excitation. These side-pumped MSM TWPDs also have a better efficiency (>5%) compared with LTG-GaAs based MSM vertically-illuminated photodetectors. Without complex isolation process or E-beam lithography, this novel device is easily fabricated and offers a better way than p-i-n TWPD or MSM VPD to be integrated as TWPD array for high power THz emitters.