Recombination of donor bound-excitons in germanium

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Abstract
The decay of the luminescence intensity associated with the LA-phonon-assisted recombination of free excitions in germanium is measured for samples with different donor concentrations. Simultaneously, the decay of the luminescence intensity originating from recombination of donor bound excitons is investigated. All measurements are carried out at temperatures where condensation into electron-hole droplets cannot be expected, i.e., above the critical temperature of 6.54 K. To exclude influences of electron-hole plasma the excitation power was also chosen low. The dependence of the experimental lifetimes on the arsenic donor concentration, as well as on the temperature, can be described by a system of equations including capture of free electrons into bound excitons and thermal dissociation of bound excitons into free excitons. The bound-exciton lifetime is determined to be 1.25 μsec in the As-donor case. Comparison of the experimental value to theoretical estimates of the exciton lifetimes leads to the conclusion that phonon-assisted Auger recombination must be a very effective channel for donor-bound-exciton decay.