[Physical implementation of computer] One-Way conductivity of PN Junction

PreviousArticleThis article introduces what is a pn. Next, let's talk about the features of a pn.

There are three main things: 1 is the one-way conductivity of the pnjunction, 2 is the volt-ampere characteristic of the pnjunction in the circuit, and 3 is the capacitance effect of the pnjunction. Write in three articles.

The first is unidirectional conductivity.

Connect the pnns to the circuit to see what will happen.

There are two cases to discuss the connection of Pn to the circuit. One is p type semiconductor connected to the positive electrode. This method is called forward bias. The other is the n-type semiconductor positive electrode. This method is called reverse offset.

Let's first look at the positive offset.

When the positive offset is used, the electrons in the P zone will run to the positive pole of the power supply, so the negative ions will be reduced because some electrons are lost in the P zone. Similarly, the power supply will make the electrons move from the negative pole to the N zone. In this way, the electrons lost due to the diffusion of the N zone will also be reduced. In this way, because the negative ions in the P zone and the positive ions in the N zone are reduced, the whole space charge zone is narrowed, or the inner electric field is reduced. However, if the voltage is not very large, the circuit can only have a certain amount of current. We know that the current size is the number of electrons that can run in a unit of time. When the extra voltage is not large enough, the electronic speed will be so high, then, the electrons that slowly spread from zone N will run to the positive pole of the power supply and pile up in Zone P, which in turn will increase the inner electric field and form a new dynamic balance. However, due to the extra voltage, this result narrowed the space charge zone. In addition, when the applied voltage reaches a certain level, the Space-Time Zone will disappear completely. The critical voltage value that completely disappears from the space charge zone is called the conduction voltage. In short, when the positive offset of the PN junction, the current size depends on the applied voltage. As a result, a large amount of electrons can form a large forward current due to zone N doping.

 

Let's look at it again.Reverse offset.

In reverse bias, both the holes in Area P and the electrons in area n move far away from the PN knot to both sides. The negative ions in the P zone and the positive ions in the N zone increase, that is, the whole space charge zone gets thicker. Because the action of the outer electric field is the same as that of the inner electric field, it will hinder the diffusion and increase the drift. In this case, only the electrons intrinsic in the P zone are moved. Because the number is very small, only a small reverse current can be formed. This current is small enough to be negligible.

 

The final characteristic is that a large positive current can be formed in the forward offset, and only a small reverse current can be formed in the reverse offset. Therefore, the PN junction has unidirectional conductivity.

 

The reason for the positive offset is the forward current, and the reverse offset is the reverse current. There is no special reason for this. It is just a habit of people, because the forward offset current is relatively large, and the reverse offset is almost no current.