EFFECTS OF DANGLING BONDS ON THE RECOMBINATION FUNCTION IN AMORPHOUS-SEMICONDUCTORS

A closed-form expression for the recombination function in steady-state illuminated hydrogenated amorphous silicon (a-Si:H) is given for the case that recombination occurs mainly via the dangling-bond states. Based on the three charge conditions (positive, neutral or negative) for the dangling bonds, the three corresponding occupation functions are derived; an expression for the recombination function R(DB) is thereby obtained. The latter differs considerably from the commonly used Shockley-Read and Hall function R(SRH). As an illustration, the limiting carrier in an a-Si:H p-i-n solar cell under reverse voltage is shown to be either one with a longer drift length, using R(SRH), or one with a shorter drift length, using R(DB). Therefore one can conclude that the use of the proper recombination function is critical for a discussion of the relevant physical parameters involved in the description of p-i-n devices. Interpretation for ambipolar diffusion length and photoconductivity are also mentioned as cases where the use of the appropriate occupation and recombination functions are of decisive importance.