The influence of spatial variations of diffusion length on charge collected by diffusion from ion tracks

Charge collected by diffusion from ion tracks in a semiconductor substrate may be influenced by the substrate diffusion length, which is related to recombination losses. A nonuniform spatial distribution of recombination centers results in a nonuniform diffusion length function. A theoretical analysis shows that, excluding some extreme cases, charge collection is insensitive to spatial variations in the diffusion length function, so it is possible to define an effective diffusion length having the property that collected charge can be approximated by assuming a uniform diffusion length equal to this effective value. Extreme cases that must be excluded are those in which a large number of recombination centers are confined to a narrow region near the substrate boundary.