Signal and Noise Characteristics of Terahertz Frequency-Selective and Broadband High-Tc Josephson Detectors

Josephson detectors based on YBa₂Cu₃O_7-x [100]-tilt bicrystal junctions were fabricated and their frequency-selective and broadband modes of operation were studied at terahertz frequencies. The resistances of the [100]-tilt junctions were in the range of 1-200 Ohm and their characteristic voltages were up to 8 mV at 4.2 K. Values of the responsivity up to at radiation frequency of 0.7 THz were demonstrated for the low-resistance frequency-selective detectors at a temperature of 55 K. The responsivity values were found to be in accordance with the predictions of the RSJ model, when only thermal fluctuations are considered. But, the values of noise equivalent power (NEP) and power dynamic range measured in the same experiment at a modulation frequency of 2 kHz were found to be determined by 1/f noise of the junctions and equal to 3ldr10^-13 W/Hz^1/2 and 5ldr10⁴, correspondingly. It was shown that the values of NEP of 5ldr10^-15 W/Hz^1/2 and power dynamic range of 10⁶ could be reached in this mode if high-frequency modulation or pulsed radiation were used. Broadband classical detection in high-resistance [100]-tilt junctions was experimentally found to reach the terahertz range. It follows from numerical simulations that broadband detection by the [100]-tilt YBCO junction with the resistance of 300 Ohm might be characterized by NEP-values down to 3ldr10^-15 W/Hz^1/2 and a bandwidth of 1.5 THz. Josephson detectors based on YBCO [100]-tilt bicrystal junction are promising for various terahertz applications such as real-time spectral analysis of continuous or pulsed radiation sources and terahertz imaging for medical or security screening.