Intervalley relaxation processes of shallow donor states in germanium

The role of the intervalley processes of electron-phonon interaction in the relaxation of excited shallow arsenic donors in germanium is analyzed. The rates of intracenter inter-valley transitions with emission of TA phonons in ger-manium are calculated in dependence on the uniaxial compression stress along $\{111\}$ crystallographic direction. It is shown that intervalley transitions to the ground state of the donor with emission of phonons can play a significant role in the relaxation of excited impurities only upon uniaxial stress of the crystal, since at zero stress, there are no exact resonances between impurity transitions and intervalley phonons. There are also transitions from highly excited states lying in a narrow band of energies ($\sim$ 0.5 meV) under very bottom of the conduction band to the first excited state 1$s^{(3)}$($\Gamma_5$) (in stressed germanium crystal to 1$s^{(3)}$($\Gamma_3$) state). The average rate of these transitions is estimated at 0.3 $\times$ 10$^9$ s$^{-1}$.