Figure 2

Fig 2    Schematic of sandwich structure of combined absorber and STJ.   Photons are absorbed in one of the Ta layers (usually the top layer) and cause a tunneling current.   The second diagram shows a lateral device in which the quasiparticle charge divides, diffuses in the absorber, and is trapped in the Al trap and then tunnels.  Here, Q = Q1 + Q2 ≈ 0.6 e ( E / DTa).