Time-resolved electronic capture in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>n</mml:mi></mml:math>-type germanium doped with antimony

Abstract

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 \ifmmode\times\else\texttimes\fi{} 10${}^{25}$ photons/(cm${}^{2}$ s), (ii) the lattice temperature is above \ensuremath{\sim}20 K, or (iii) a static electric field above \ensuremath{\sim}2 V/cm is applied to the crystal, the pump-probe technique reveals an additional intraband relaxation process with a characteristic time of \ensuremath{\sim}100 ps, which is much shorter than that of the capture of free electrons into the antimony ground state.