MODELING THE POWER-FLOW IN NORMAL CONDUCTOR-INSULATOR-SUPERCONDUCTOR JUNCTIONS

Normal conductor-insulator-superconductor (NIS) junctions promise to b e interesting for x-ray and phonon sensing applications, in particular due to the expected self-cooling of the N electrode by the tunneling current. Such cooling would enable the operation of the active element of the sensor below the cryostat temperature and at a correspondingly higher sensitivity. It would also allow the use of MS junctions as mi crocoolers. At present, this cooling has not been realized in large ar ea junctions (suitable for a number of detector applications). In this article, we discuss a detailed modeling of the heat flow in such junc tions; we show how the heat flow into the normal electrode by quasipar ticle back-tunneling and phonon absorption from quasiparticle pair rec ombination can overcompensate the cooling power. This provides a micro scopic explanation of the self-heating effects we observe in our large area NIS junctions. The model suggests a number of possible solutions . (C) 1998 American Institute of Physics.