Question

What is junction capacitance in a photodiode? On what parameters does its value depend?

Answer 1

$$\begin{gathered} Thejunctioncapaci\tan ceofaphotodiodeisdefinedas \\ {C}_j=\frac{{\epsilon }_{si}{\epsilon }_{0}A}{W_d} \\ where{W}_{d}isthedepletiondepthdefiendas \\ {W}_d=\sqrt{2{\epsilon }_{si}{\epsilon }_0\mu \rho (V_A+V_{bi})} \\ here \\ {\epsilon }_{si}=permittivityofsilicon \\ {\epsilon }_0=permittivityofvacuum \\ \mu =conductivity \\ \rho =carrierdensity \\ {V}_{bi}=reversebias \\ Thejunctioncapaci\tan ceisdirectlyproportionaltothediffusedarea \\ andinverselyproportionaltothewidthofthedepletionregion. \end{gathered}$$