Radiative lifetime and spontaneous emission in amorphous semiconductors

A theory for the spontaneous emission due to radiative recombination of excitons in amorphous semiconductors is presented. Four possibilities are considered: (i) both the excited electron and hole are in their extended states, (ii) the electron is in the extended and the hole in tail states, (iii) the electron is in tail and the hole in extended states and (iv) both are in their tail states. It is found that the singlet excitonic radiative recombination for possibilities (i)-(iii) occurs in the nanosecond (ns) range, and that for possibility (iv) occurs in the microsecond (?s) range. Results are compared with recent experiments and other theories.