Interaction of microwave phonons with donor electrons in Ge and Si

It has been found that small concentrations of shallow donors in Ge and Si produce relatively large amounts of attenuation of microwave phonons at low temperatures (about 1 part per million produces about 10 dB/cm attenuation at 9 GHz). A theory is given which explains the various observed temperature, polarization, and frequency dependences of the attenuation in terms of ultrasonically induced relaxation of electrons bound to the donors. It is pointed out that such measurements can give information on the energy-level seperations, symmetries, and relaxation times of bound electrons. © 1970 The American Physical Society.