Emission of terahertz radiation from InGaP/InGaAs/GaAs grating-bicoupled plasmon-resonant emitter

We have designed and fabricated an optically-pumped plasmon-resonant terahertz emitter incorporating doubly interdigitated grating gates and a vertical cavity into an InGaP/InGaAs/GaAs high-electron mobility transistor structure. The two-dimensional (2D) plasmon layer is formed with a quantum well in the InGaAs channel layer. When the dual grating gates are biased at different levels, the sheet carrier density is periodically modulated, making periodic 2D plasmon cavities along with the grating. When the device is photoexcited by laser irradiation, photoelectrons, injected to the cavities, excite the plasmons, leading to the emission of terahertz radiation. The fabricated device is subjected to 1550-nm, 1-mW (a) a single CW-laser, (b) 4-THz photomixed dual CW-laser, and (c) a 70-fs pulsed-laser illumination at room temperature. In case of (a), terahertz emission is detected by a Si bolometer under certain bias conditions, which is inferred to be due to the self oscillation stimulated by the plasmon instability. In case of (b), a resonant peak of injection-locked 4-THz oscillation is clearly observed on the device photoresponse. In case of (c), an impulsive radiation followed by relaxation oscillation is observed by electrooptic sampling, whose Fourier spectrum exhibited resonant peaks of plasmons' harmonic modes up to 4 THz. Estimated radiation power exceeds 0.1 μW, resulting in excellent conversion efficiency of the order of 10^-4.