Sensitive terahertz-wave detector responses originated by negative differential conductance of resonant-tunneling-diode oscillator

We present an experimental characterization of frequency- and bias-dependent detector responses in a resonant-tunneling-diode (RTD) terahertz (THz)-wave oscillator. By tuning the incident THz-wave frequency and the bias voltage applied to the RTD device, the origins of detection signals are identified to be two distinct detection modes. One is based on square-law detection near the peak and valley points of the negative differential conductance (NDC) region, with the detection bandwidth determined by an integrated slot antenna. The other is based on detectable current changes induced by injection locking within the NDC region when the frequency of the incident THz-wave radiation to be detected is coincident with that of the bias-dependent RTD self-oscillation between 0.74 and 0.81THz, resulting in a minimum noise equivalent power (NEP) of 7.7 pW/root Hz at 0.78THz at room temperature. Our conclusions demonstrate that an RTD oscillator can be used as a sensitive THz-wave detector within and around the NDC region.