In an n -Ge crystal uniaxially stressed along the 111 crystallographic direction, the photon echo effect has been demonstrated, and the coherence relaxation time T 2 has been estimated at ~300 ps. Nonlinear polarization leading to the effect appears due to antimony donors. Uniaxial deformation of the crystal, which is responsible for valley splitting of the donor states, significantly increases the coherence time and leads to the possibility of implementing the effect.
Zhukavin et al. (Wed,) studied this question.