Spectral properties of superconducting aluminium tunnel-diodes used as phonon generators and detectors

Using the fact, that a super-conducting tunnel diode, used as phonon detector, can only detect phonons with higher energies than a certain energy barrier, information of the emitted spectrum can be obtained in experiments where phonons are emitted and received. For such measurements, the preparation of aluminium diodes with an increased energy gap was developed. Also a 3He immersion cryostat has been designed, allowing measurement at temperatures slightly lower than 0.3 K. In the experiments using two aluminium tunnel diodes (transmitter and detector), produced on opposite sides of an insulating single crystal by evaporation, mainly the relation between signal amplitude and transmitter-receiver characteristic), time constants of the detector are measured and absolute values of the signal amplitude are calculated. In order to compare the experimental results with theoretical predictions a computer code is developed for simulation of the different competing processes occuring within the framework of BCS theory. These results agree with the experimental findings; especially the observed additional effects caused by finite excitation concentrations and finite injection. (orig./HPOE)