ANTIREFLECTIVE COATING FOR BIPBSRCACUO SENSORS

The applications of high T-c superconductors as transition edge bolome ters or room temperature thermopiles appear most promising at the long infrared wavelengths, However, the sensor performance at these wavele ngths is impeded by the large reflectance of superconductor films, In this work, effects of antireflective coating on the performance of BiP bSrCaCuO sensors were investigated, Thermal evaporation was used to de posit semiconductor CdS onto sputtered BiPbSrCaCuO films, It was found that, in order to achieve transparent and uniform CdS coating, it was necessary to maintain the substrate temperature al 180 degrees C duri ng the evaporation, The superconductivity of BiPbSrCaCuO appeared to b e not degraded by the deposition of CdS. After the deposition of CdS w ith a nearly optimum thickness, the reflectance of BiPbSrCaCuO sensor was reduced from 0.8 to below 0.4 for wavelengths above 10 mu m, In ad dition, the temperature coefficient of the Blm resistance was seen to increase in the transition region, The increases of film absorptance a nd resistance were consistent with the change of bolometric responsivi ty of the coated sensor. The use of Ge semiconductor for antireflectiv e coating was also studied, A reflectance of 0.16 was achieved at wave lengths near 10 mu m on Ge coated sensors, This small reflectance was in good agreement with predictions derived from the computed optical c onstants of BiPbSrCaCuO films.