Recombination ina-Si: H: Transitions through defect states

Abstract

To obtain detailed information about recombination processes near room temperature in $a$-Si: H we have measured the steady-state and transient response of luminescence, light-induced ESR, and photoconductivity in lightly doped and undoped samples. The low-energy luminescence is at a different energy in $n$- and $p$-type $a$-Si: H, and has an intensity-dependent decay. The results lead us to propose a new model—that the radiative transition is the capture of a majority carrier into a neutral dangling bond, having a low radiative efficiency and only a small Stokes shift. Measurements of the quantum efficiency for generating light-induced ESR (or LESR) confirm that a transition through a dangling bond is the dominant recombination mechanism in all samples, and is predominately nonradiative. We discuss the trapping mechanism and conclude that a single multiphonon process does not seem possible. Instead we suggest that the mechanism may be a cascade through as yet unidentified excited states. Transient luminescence, LESR, and photoconductivity each show that the response time is much longer in doped samples than in undoped samples.