COMPARISON OF GENERATION AND RECOMBINATION LIFETIMES IN HIGH-RESISTIVITY SILICON

Generation and recombination lifetimes have been theoretically studied for the case of high-resistivity silicon on the basis of the Shockley-Read-Hall model. Thanks to the high resistivity of silicon, it has been possible to take into account only the generation-recombination levels which are situated between the Fermi level E(F) and the level E(F)' symmetrical to E(F) with regard to the midgap. First, a simple approach based on the presence of a single generation-recombination level in the band gap has been considered; however, its validity is fair because chemical analyses of high-resistivity silicon show that several levels with energy close to midgap or to the boundaries E(F)-E(F)' are generally present. This means that levels which are located at different positions in the gap may influence the generation and recombination lifetimes tau(g) and tau(r) but are not taken into account by such a model. In order to overcome this difficulty, a two-level model has been developed. The main result is that the ratio of tau(g)/tau(r) should range between 1 and 10. Experimental confirmation of this later model has been obtained by measuring the two lifetimes tau(g) and tau(r) whose resulting ratio was found to be within the limits 1-4.