Phonon echoes from acceptors in silicon.

Coherent microwave acoustic excitation of the inhomogeneously broadened state of the neutral acceptor In in crystalline Si has resulted in the first observation of phonon echoes below 0.1 K. The echoes allow a quantitative determination of the acceptor dephasing times, radiative lifetimes, and acoustic deformation potentials. In addition, the temperature-dependent sound velocity provides information on the inhomogeneous linewidth of the ground state in highly perfect crystals.