Photon Echo in Uniaxially Stressed Germanium with Antimony Donors

Photon echo is observed in n-type Ge uniaxially stressed along the [111] crystallographic direction, with a coherence relaxation time of 300 ps. The nonlinear polarization responsible for the effect originates from antimony donors. Uniaxial stress induces valley splitting of the donor states, substantially enhancing the coherence time and enabling the observation of photon echo.