| Compared with existing semiconducting p-n junction x-ray detectors, superconducting tunnel junctions offer superior energy resolution in the detection of single photons. Such superconducting detectors are desirable for x-ray astronomy applications, where the photon flux is low and high energy resolution is required. Progress is reported on the development of NbTa-Al-AlOx-Al tunnel junction structures for the observation of celestial x-ray sources. These devices use superconductor "bandgap engineering" for quasiparticle trapping to enhance performance. Experimental results at 0.3 K are presented, showing energy resolution better than 200 eV full-width-half-maximum for 6 keV x-rays. The absorption efficiency of these devices is better than 25%, with active areas of {dollar}rm{lcub}approx100{rcub} mu mtimes100 mu m.{dollar} The devices are designed to easily scale to larger areas and absorption efficiencies. Significant improvement in the device energy resolution appears possible with only minor modifications. |
