The capacitance of a pn junction depends on the width W of the depletion layer.

If the junction is heavily p-doped then it will be an asymmetric p⁺n junction where N_a >> N_d. In this case the total depletion width is approximately equal to the depletion width on just the n-side of the junction.

To experimentally characterize a pn-junction, often the capacitance is measured as a function of the applied voltage. For an abrupt p⁺n junction, a plot of 1/C_j² versus V is a straight line. The formula can be determined from the above two equations. The slope and intercept of this line give the doping concentration and built-in potential.

The capacitance-voltage characteristic of a silicon p⁺n-junction with an area of 0.005 cm² is measured. The results of this measurement are shown in the table on the right.

What is the doping concentration and the built-in potential?

The dielectric constant of silicon is ε_r = 11.9.