Lifetime distribution of the photoluminescence of a-Si:H and a-Si1−xCx:H

Abstract The lifetime distribution of the photoluminescence of a-Si:H and a-Si 1−x C x :H has been studied by frequency resolved spectroscopy in the temperature range 10–100K. The experiments are performed on undoped and doped films and the defect density N d is varied by electron bombardment and stepwise annealing. In undoped a-Si:H (low N d ) the lifetime distribution consists of a single broad structure which is dominated by a peak at τ ≈ 10 −3 s (excitation density 5·10 15 cm −2 s −1 ). The maximum of this distribution shifts to shorter times when the excitation intensity increases, which is difficult to reconcile with geminate pair recombination. An increased temperature causes very similar changes: in the range 10–80K the peak position moves from 10 −3 s to 3·10 −4 s. Most surprisingly, the decrease of the PL-intensity due to additional defects is not connected with a shift of the lifetime distribution. We conclude that defects introduce a fast non-radiative channel which does not compete on the time scale of this experiment.