Diffusion Capacitance
Deflection layer capacitance-reverse junction when forward biased another contribution from rearrangement of minority carrier density-Diffusion capacitance Applied voltage
Current  |
 Forward Bias
 Small signal amplitude
Small signal as component of hole density in n
For 
.
Similar expression for electron density in p side.
Now for holes n in n side we know that continuity equation is S
Thus
Or
Non Time varying case  |
So here
effect of frequency dependence
Small signal current 
 admittance due to diffusion only 
low frequency 
low frequency
 and  are function of bias frequency.  so deflection layer  capacitance will dominate at high frequencies.
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