MATERIAL ASPECTS FOR PREPARING HTS QUASI-PARTICLE INJECTION DEVICES

Quasiparticle (QP) injection devices based on HTS could play an import ant role in future superconducting applications if material aspects ca n be better controlled. One reason why this kind of device received li ttle attention in the past is the lack of an appropriate barrier for Q P tunnelling. In a series of experiments, we used different barriers t o test if they are suitable, i.e. if a current and possibly a voltage gain can he achieved. We improved the performance of planar YBCO/natur al barrier/Au devices and a current gain of more than 6 at 40 K was ob served. Most devices, however, showed signs of heating effects. Anothe r barrier material was SrTiO3 with layers of 5-6 nm thickness. Current -voltage characteristics showed that the barriers were continuous and we observed current gains of up to 3 at 60 K. PrBa2Cu3O7-x is an inter esting candidate if one could overcome the problem of resonant inelast ic tunnelling for QP. In a series of experiments we demonstrated that, even for 3 nm thin PBCO barriers on a- and c-axis oriented YBa2Cu3O7- x, most devices showed at best a current gain of 1. However, we have i ndications that a current gain of 10 could be possible with unity volt age gain.