Ec. Kirk et al., Impact of the absorber and absorber/trap interface quality on the resolving power of STJ X-ray spectrometers, NUCL INST A, 444(1-2), 2000, pp. 201-207
We fabricated X-ray detection devices by instrumenting 2 Al/AlOx/Al/Nb tunn
eling junctions at each end of strips of epitaxial Ta. The Ta strip acts as
photon absorber and is a few hundreds of microns long, the Al layers act a
s quasiparticle traps. The quality of the epitaxial Ta thin film as well as
the absorber/trap interface was varied. Devices kept at 550 mK and biased
around 300 mu V were irradiated by 6 keV photons. The total charge collecte
d by both junctions varies with the energy released by absorbed photons, de
pends on various quasiparticle loss processes, and is a function of the bia
s voltage of the tunneling devices. Our arrangement enables to distinguish
between energy resolution degrading mechanisms occuring in the Ta absorber
and those present in the vicinity of the tunneling junctions. (C) 2000 Else
vier Science B.V. All rights reserved.