Substrate contribution to the surface impedance of HTS films on Si

We study the effects of semiconductor substrates on the surface impedance of high-T-c Superconductor (HTS) YBa2Cu3O7-delta (YBCO) films. The characteristic impedance of silicon (Si) ( for different doping levels and for different charge carrier scattering times) is evaluated. In particular, the most relevant features of Si electrodynamics are highlighted by the introduction of suitable normalized quantities. The effective surface impedance of the YBCO films on Si substrates is then calculated and discussed for different temperatures and frequencies in the microwave range, comparing the obtained results to their limiting expressions for bulk and thin-film HTS. Our analysis shows how the widely used thin-film approximation for the surface impedance can fail, critically highlighting the conditions it requires to be correctly used. We show that substrate contributions can heavily influence the overall response.