Donor-Acceptor Pair Recombination Involving the First Excited State of a Donor in GaAs

The photoluminescence spectrum of epitaxially grown $n$-type GaAs in the vicinity of the band-gap energy shows peaks whose temperature dependence and energy separations suggest the existence of pair recombination radiation involving the ground state and first excited state of a donor. Calculation based on this model and the use of hydrogenic wave functions for the ground state and the first excited state of the donor indicate that the recombination radiation arises from donor-acceptor pairs whose most probable separation is about 420 Å. This number is in reasonable agreement with the expectation based on the measured room-temperature conductivity of the sample.