Relaxation of the Excited States of Arsenic in Strained Germanium

The relaxation times of the lower p states of the arsenic donor in a germanium crystal strained along the [111] crystallographic direction are studied. Measurements are performed by the pump–probe method, using free-electron laser radiation. The states are excited from the 1s (Γ1) ground state. The experimentally measured decay times of the 2p0, 3p0, and 2p± states are 1.3, no more than 0.2, and 0.4 ns, respectively. It is shown that the relatively high relaxation rate of the 2p± state is defined by the interaction with intravalley TA photons.