Formation and decay of positron states in semiconductors

Positronium capture by point acceptors and dipoles (negatively charged acceptor-positively charged donor) in semiconductors at low temperatures is considered within the frames of the cascade theory of capture. Cross section of positronium capture in germanium at 100K turned to be equal to 1.1x10sup(-15) cm2, while in silicon it was equal to 3.75x10sup(-14) cm2. Temperature dependences for the cross section of positronium capture by the dipole are shown to have the form σ approximately Tsup(-2) and by negatively charged acceptors - they have the form of σ approximately Tsup(-3). Probabilities of P(E) adhesion and thermal ionization of 1-P(E) positronium from highly excited states are calculated. For example, at E=1 MeV the value 1-P(E) at room temperature is close to zero, while at hydrogen temperature it is close to one