QUASI-PARTICLE LIFETIMES AND TUNNELING TIMES IN AN SS'IS''S TUNNEL JUNCTION DETECTOR

A tunnel junction detector with artificial trapping layers, S' and S'' , near the tunnel barrier can be described as an SS'IS''S structure. G ap reduction takes place in S due to the proximity effect with the S' (S'') layer. Effective trapping, excitation and tunneling rates of the reduced gap region in the junction are calculated as a function of th e operating temperature and junction bias voltage on the basis of a mi croscopic model of the proximity effect in the SS' sandwich. The calcu lations are done under the assumption that the thickness of the S' lay er d(s') is small compared to its coherence length xi(S'), and dirty l imit conditions are fulfilled for both the S and S' metals. The limits of applicability of these approximations are discussed by calculating corrections to the space dependence of the order parameter in S and S ' due to a) finite thickness d(s') of the S' layer and b) for large me an free path l(s,s') in the S and S' layers.