Measurement of hole diffusion length in heavily doped n-type silicon using SEM

Abstract

The minority carrier diffusion length is measured in heavily doped silicon substrates of n+–n epitaxial wafers. Each sample is converted to a one-sided n+–p junction by diffusion of boron through the thin n-region. The junction is angle-lapped and the electron beam of a scanning electron microscope is used to inject excess electron–hole pairs in the n+–region. The hole diffusion length is deduced from the variation of the electron beam induced current (EBIC) as a function of distance from the junction. The minority carrier lifetime is obtained from the measured data using the values of hole diffusion constant in heavily doped n-type silicon. A plot of hole lifetime τp as a function of dopant concentration reveals that the band-to-band Auger effect becomes the dominant recombination mechanism for dopant concentrations in excess of about 2 × 1019 cm−3.