depletion capacitance

[ykishore]

What happens to the depletion capacitance in a pn junction dide when the reverse bias voltage is increased!!!!!!!!!!!!

 

[djalli]

Theoretically depletion capacitance varies inversely with the voltage drop from N to P regions so when reverse bias voltage is increased.

It has a nonlinear relationship but you can usually approximate as linear which is dropping as reverse bias is incleased.

It looks like a curved-straight line.

 

[yjkwon57]

Major carriers to flow across the junction are further blocked and minor carriers are allowed to flow more easily. The number of carriers to flow across the junction can be determined statistically.

 

[DJ]

This is correct.
You can look at the PN junction as two plat of a capacitor(Actually for a step junction the C(V) expression is the same). There is a depletion range for a PN junction without any bias voltage. The high E feild rejects the electrons and holes back and stop the difusion. So without any bias the E feild force is equal to the difusion "force" . When you reverse bias the junction, the depletion range is increased (the two capacitor plats are moved farther) and the capacitance is reduced. Varactor is a PN junction that its capacitance goes down as you increas the reverse bias.
C(V) curve is not linear at all. For step junction C(V) acts as 1/V^0.5.
There are complicated PN junctions for different applications and their C(V) is of course different. For example SRD (step recovery diode) there is very sharp change of the C as a function of V in order to create a step function that couses to a comb of harmonics to very high frequency. There are different kind of varactors (abrupt, hiperabrupt, linear etc.) that have different C(V) curve but for all of them C goes down as te reverse bias voltage goes up.

 

[krashkealoha]

Another scenario is where your p-region, where the bias is being applied, has a much lower concentration with respect to the n-region. Since space-charge neutrality must be met, you will see very little to no change in depletion capacitance with increasing reverse bias voltage.

 

[djalli]

see picture!

 

[savadi]

If the reverse bias of a p-n junction is incresed the lengh of depletion area is incresed also. As you know if the distance between the plates of a capacitor is incresed, the value of capacitor whould be reduced. this efect can be simillary happens about the depletion capacitor. so if the reverse bias voltage of p-n junction is incresed depletion capacitor would be decreased. the relation between C and V is like this:
C proprtional 1/(square root of V)