MEASUREMENT OF HOLE DIFFUSION LENGTH IN HEAVILY-DOPED N-TYPE SILICON USING SEM

The minority carrier diffusion length is measured in heavily doped sil icon 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-reg ion. The junction is angle-lapped and the electron beam of a scanning electron microscope is used to inject excess electron-hole pairs in th e n+-region. The hole diffusion length is deduced from the variation o f the electron beam induced current (EBIC) as a function of distance f rom the junction. The minority carrier lifetime is obtained from the m easured data using the values of hole diffusion constant in heavily do ped n-type silicon. A plot of hole lifetime tau(p) as a function of do pant concentration reveals that the band-to-band Auger effect becomes the dominant recombination mechanism for dopant concentrations in exce ss of about 2 x 10(19) cm-3.