CHARACTERISTICS OF THE ELECTRICAL RESPONSE OF YBCO FILMS WITH DIFFERENT MORPHOLOGIES TO OPTICAL IRRADIATION

We have fabricated YBCO films of varying thicknesses (300 angstrom - 3000 angstrom) and morphologies, and measured their electrical response to optical radiation. We report on these measurements, emphasizing the dependence on temperature, light chopping frequency, and cryogenic environment. The temperature dependence of the film resistance is determined in part by the film morphology. This morphology may be represented by a simple model consisting of a two-dimensional array of coupled grains. The magnitude of the bolometric response correlates as expected with the sharpness of the superconducting transition. The increased response observed at lower temperatures (non-equilibrium?) correlates with the temperature dependence of the resistance above the transition. These measurements and observations lead to a proposed optimization scheme to maximize the low-temperature response and fully explore the potential for fast non-equilibrium detectors.