Time-resolved electronic capture in n-type germanium doped with antimony

Kurzfassung

The low temperature (T=5–40 K) capture of free electrons into hydrogenlike antimony centers in germanium has been studied by a time-resolving experiment using the free electron laser FELBE. The analysis of the pump-probe signal reveals a typical capture time of about 1.7 ns that decreases with pump energy to less than 1 ns while the number of ionized donors increases. The dependence on the pump-pulse energy is well described by an acoustic phonon-assisted capture process. In the cases when (i) a significant number of the electrons is in the conduction band (flux densities larger than 5× 1E25 photons/(cm2 s), (ii) the lattice temperature is above ~20 K, or (iii) a static electric field above ~2V/cm is applied to the crystal, the pump-probe technique reveals an additional intraband relaxation process with a characteristic time of ~100 ps, which is much shorter than that of the capture of free electrons into the antimony ground state.