Low-Noise Resonant Tunneling Diode Terahertz Detector

This article presents a comprehensive analysis of indium phosphide (InP) triple-barrier resonant tunneling diodes (TB-RTDs) operating as direct terahertz (THz) detectors at zero bias. Through analytical derivation, the influence of device dimensions and of current–voltage curvature on voltage responsivity and noise equivalent power (NEP) is explored, and theoretical expressions for diode sensitivity are derived. On-wafer measurements of two scaled TB-RTDs with top contact areas of 0.5 and $1 \,\mu \mathrm{m}^{2}$ are conducted, followed by a comparative analysis, including harmonic-balance simulation results based on a self-developed TB-RTD nonlinear model. The measurements reveal that the responsivity scales with device area, as predicted by the theory, with a peak responsivity of 2123V/W at 340 GHz for the TB-RTD, and above 1200V/W across the entire WR2 band (330–500 GHz) for the smaller $0.5 \,\mu \mathrm{m}^{2}$ area device. The NEP values do not exceed 3.5 and $2 \,\mathrm{pW}/{\sqrt{\text{Hz}}}$ for the 1 and $0.5 \,\mu \mathrm{m}^{2}$ devices, respectively, with the lowest measured NEP being $1.15 \,\mathrm{pW}/{\sqrt{\text{Hz}}}$ for the $0.5 \,\mu \mathrm{m}^{2}$ device. These sensitivity values place the TB-RTD at a level comparable with the state-of-the-art THz direct detectors operating at room temperature. The investigation offers a clear picture of the intrinsic performance of TB-RTD operating at zero bias, with a detailed overview of the on-wafer measurement setup, power characterization method, and detector figures of merit, highlighting the potential of TB-RTDs as compact, power-efficient, and ultrasensitive direct THz detectors.