Conventional and novel approaches to RF power generation with two-terminal devices at terahertz frequencies

Recent advances in design and technology significantly improved the performance of low-noise InP Gunn devices in oscillators at W-band (75-110 GHz) and D-band (110-170 GHz) frequencies. More importantly, they resulted in orders of magnitude higher radio-frequency (RF) output power levels above D-band. Examples are continuous-wave RF power levels of more than 30 mW at 193 GHz, more than 3 mW at 300 GHz, and more than 1 mW at 315 GHz. The DC power requirements of these oscillators compare favorably with those of RF sources driving frequency multiplier chains to reach the same output RF power levels and frequencies. Generation of significant RF power levels from InP Gunn devices is predicted up to at least 500 GHz. A different approach to a Gunn-like device for even higher frequencies is based on a heterostructure perpendicular to a superlattice. Tunnel injection transit-time (TUNNETT) diodes are another candidate for low-noise RF sources at submillimeter-wave frequencies. Low-noise GaAs TUNNETT diodes, for example, already yielded more than 10 mW at 202 GHz, but more recent material systems such as GaN show more favorable material parameters than GaAs.