EFFECT OF SHORT-RANGE POTENTIAL AND COUPLING WITH PHONONS ON IMPURITYSTATES

An influence is discussed of a short-range potential and a coupling wi th phonons on the energy spectrum of donors. It is shown that the incr easing attractive short-range potential leads to an additional state o f s symmetry, in which the electron is more strongly localized than in the other states. The energy level connected with this state and hydr ogen-like donor levels exhibit an anticrossing with a shape dependent on the electron-phonon interaction. For sufficiently small phonon ener gy, the anticrossing becomes very sharp. This additional state coexist s with the hydrogen-like states, which can lead to a metastability of donors.