where formula_38 is the relative dielectric permittivity of the semiconductor, formula_39 is the built-in voltage, and formula_16 is the applied bias. the depletion region is not symmetrically split between the n and p regions - it will tend towards the lightly doped side. a more complete analysis would take into account that there are still "some" carriers near the edges of the depletion region. this leads to an additional -2kt/q term in the last set of parentheses above.