Evaluation of Cavity Modes in Superconducting Intrinsic-Josephson-Junction Oscillators for Terahertz-wave Generation

To realize antenna-coupled terahertz (THz)-wave oscillators using intrinsic Josephson junctions, rectangular mesas, 98-158 μm long, 78 μm wide and 1.04 μm high were fabricated on a Bi₂Sr₂CaCu₂O_8+δ high-temperature superconductor, and the cavity resonant modes in the mesas were evaluated based on their radiative frequencies. For appropriate bias voltages in the return curve of an I-V characteristic of a 138-μm-long mesa, two peaks in the radiative power were observed. At the voltages where the peaks first appeared at high and low biases, frequencies of 0.646 and 0.499 THz were measured using a lamellar interferometer. The cavity modes corresponding to these two frequencies are TE₁₂₁ and TE₁₁₁ modes, respectively. The temperature and size dependencies of the calculated resonant frequencies based on a 3D cavity model agree with measurements, validating the mode assignments.