[Physical implementation of the computer] capacitance effect of the pn

First, review what determines the capacitor size of a capacitor.

Three factors: 1. dielectric material between two electrode plates; 2. area facing the two electrode plates; 3. Distance between the two electrode plates.

The PN junction is equivalent to a capacitor. The space charge zone is equivalent to the intermediate medium, and the P zone and N zone are equivalent to two electrode plates.

As we have already mentioned above, when the forward offset is used, the space charge zone decreases as the voltage increases. The reverse bias Space-Time Zone will increase with the increase of voltage. This change in the space charge zone is called a barrier capacitor.

In addition, when the positive bias occurs, the electrons in area n will spread from the vicinity of the PN knot to the P zone. In addition, the electrons that spread from zone N to zone P gradually compose with holes from the place close to the PN knot. The closer the area to the PN knot, the more composite. Then the positive and negative charges of zone N and zone P will decrease progressively from the PN knot. The charge concentration on both sides of the PN junction increases with the increase of voltage. This will also lead to changes in capacitance. This kind of capacitance changed due to the diffusion movement is called the diffusion capacitor.

The capacitance of the PN junction is equal to the sum of the Barrier Capacitance and the diffusion capacitance. In short, the capacitance of the entire PN junction changes with the change of the applied voltage. This feature is called the capacitance effect.