Terahertz Emission from Resonant Tunneling Diodes without Satisfying Oscillation Condition

Terahertz (THz) emission from resonant tunneling diodes (RTDs) is normally obtained under the oscillation condition in which the negative differential conductance (NDC) exceeds the circuit loss. In this study, we show that a relatively broad band THz emission was observed even for RTDs with an NDC smaller than the circuit loss. The observed output power was on the order of 1–10 nW at 1.2–1.9 THz with spectral widths of 50–100 GHz. The observation was reasonably explained by the theoretical calculation based on the shot noise amplified by the NDC. This emission corresponds to the amplified spontaneous emission in optical devices.