Active two-terminal devices for terahertz power generation by multiplication

Devices from two major groups of active two-terminal devices, i.e., transit-time diodes and transferred-electron devices, have been employed successfully to generate RF power levels of more than 1 mW at frequencies above 200 GHz. The extraction of higher harmonics from the internal frequency multiplication in these inherently nonlinear devices has often been the means for reaching submillimeter-wave frequencies. The RF power levels at high millimeter-wave and even submillimeter-wave frequencies are also high enough to reach higher terahertz frequencies with external frequency multiplication. At frequencies up to 300 GHz, Si IMPATT diodes yielded the highest RF power levels from any fundamental solid-state source, e.g., 50 mW at 245 GHz and 7.5 mW at 285 GHz. However, the RF power of more than 1 mW from InP Gunn devices around 315 GHz is the highest from any such fundamental RF source above 300 GHz. GaAs TUNNETT diodes yielded 100 5 mW in the fundamental mode at 100-107 GHz. Operating as efficient self-oscillating frequency multipliers, they generated RF power levels of more than 10 mW at 202 GHZ and more than 4 mW at 235 GHz. GaAs IMPATT diodes, e.g., yielded 2 mW at 232 GHz and 1 mW at 242 GHz. This paper reviews the power generation capabilities and basic properties of these two-terminal devices as fundamental RF sources. It compares the above-mentioned devices, but also other two-terminal devices such as RTDs and SLEDs directly at the RF power level, but also in terms of RF power per unit area as a figure of merit. The paper also compares up-conversion efficiencies and dc power consumption of these two-terminal devices.