Recombination dependent characteristics of silicon P+−N−N+ epitaxial diodes

The low level injection d.c. and transient characteristics of a P+−N−N+ diode are discussed from a theoretical point of view, using the minority carrier lifetime ‘τepi’ in the lightly doped region and the parameter α defining the properties of the high-low junction, as basic parameters. A value of α less than unity is predicted for typical epitaxial silicon structures. Detailed experimental studies involving both lifetime measurements (using optical techniques) on the original epitaxial layer and substrate and d.c. plus transient measurements on completed devices confirm the existence of a ‘blocking’ high low junction (α less than unity). However the measured value of α is still considerably higher than that predicted from the theory, thus indicating conclusively the presence of additional recombination mechanisms at the high low junction interface. An interesting and useful result of the study is the fact that using a combination of d.c. and transient measurement techniques, both α and the effective epitaxial layer width Wepi can be uniquely determined using the given theoretical curves.