Capacitance measurements of p-n junctions: depletion layer and diffusion capacitance contributions

A set of capacitance measurements is proposed to identify the different contributions to the junction capacitance (diffusion capacitance and depletion layer capacitance) of p-n Si diodes. By measuring the C-f and C-V characteristics of Si commercial diodes, we fully characterize the AC behaviour of such devices. At reverse bias voltages, only the depletion layer capacitance is present and it is frequency independent in our range of measurement (up to 13 MHz). From C-V characteristics, we deduce a linearly graded junction nature and a built-in value of 0.59 ± 0.02 V. At forward bias voltages and frequencies lower than 100 kHz, both the diffusion and the depletion layer capacitances contribute to the junction capacitance. A simple calculation allows us to obtain a value for the average minority carrier lifetime of tau = (4 ± 2) × 10 -6 s. Finally, a voltage dependence of exp( qV /2 kT ) is deduced for the diffusion capacitance.