[Physical implementation of computers] root of electronic technology-pn

PreviousArticleThis article describes what P-type semiconductors and n-type semiconductors are. What if p-type semiconductors and n-type semiconductors are put together.

Note: as to why we should discuss how they are put together, it is because the basic structure of diodes is to put them together. In short, let's talk about how they will be put together.

If we put a P-type semiconductor and an n-type semiconductor one left and one right on a substrate, it will look like this.

The left is P-type semiconductor, And the right is n-type semiconductor. The small dots on the left represent holes, and the small black dots on the right represent free electrons. Of course, because both p-type semiconductors and n-type semiconductors may also generate a few free electrons and holes due to temperature or light, there are a few small black spots in the left diagram and a few small dots in the right diagram.

So what does the negative number on the left and the positive number on the Right mean? To explain the positive and negative signs, we take the P-type semiconductor mixed with boron in silicon as an example. Its electronic structure.

We call the doped boron atoms as impurity atoms. We know that each silicon atom and the four silicon atoms around it form a stable structure by forming a bond. We also know that the outermost layer must be eight electrons, which is a stable structure. The impurity atoms and the silicon atoms around the formation of a bond still lacks an electron, so a hole is generated. This hole will attract the electrons of the more active silicon atoms nearby to fill in, so the impurity atoms are represented by a negative sign because the negative electrons of the Electronic Band become the negative ions that cannot be moved.

Then let's talk about n-type semiconductors. The electronic structure is as follows:

N-type semiconductors are mixed with 5-price impurity atoms, so the impurity atoms form a bond with the surrounding silicon atoms and an extra electron. The extra electrons are not bound by the crossbond because they are not involved in the formation of the crossbond. So we only need to absorb a small amount of energy. This electron becomes a free electron and runs out. The impurity atoms, because of the loss of electrons, turn into positive ions that cannot be moved, so they are represented by the positive signs.

 

Well, I have already explained the first figure, and I would like to remind you that P-type semiconductors and n-type semiconductors are both electrically neutral.

Next we will analyze the reason for the problem.

First, we have mentioned that the intrinsic electrons and holes are paired, And the impurity atoms mentioned above will inevitably lose the electrons when absorbing one electron. All in all, we can conclude that the positive charge is always equal to the negative charge, so the entire p-type semiconductor is electrically neutral. The principle is similar. It can be seen that n-type semiconductors are also electrically neutral.

Okay, I have pointed out both the description and attention. Let's look at what if we just put p-type semiconductors and n-type semiconductors together without adding any interference to them?

The answer is that the free electrons in the n-type semiconductors on the right are much higher than the P-type semiconductors on the left, so the free electrons on the right will spread to the left, which is called the diffusion movement. Then the electrons that spread from the right side to the left will fill the holes on the left side.

Result

In this case, the electrons running on the right fill the holes on the left, and the negative ions are left on the left, and only the positive ions are on the right. In this way, both sides of the power are damaged and the opposite charge is displayed, an inner electric field will be generated. We know that the direction of the electric field is positive and negative, therefore, the inner electric field is directed to the left on the right. Because the existence of the inner electric field will make the electrons on the left and the electrons on the left run to the right under the action of the electric field. This is called the drift movement. At the same time, the inner electric field will also inhibit the electron from right to left, that is, it will inhibit the diffusion movement.

Shows the status. The area of the red line in the figure represents the inner electric field.

Of course, at the beginning, the number of electrons on the left is relatively small, so the drifting motion must be less than the diffusion motion. However, as more and more electrons run from the diffusion movement to the left, the negative charge on the left and the positive charge on the right are increasing, the inner electric field is getting stronger and stronger, the drifting movement and the suppression of the diffusion movement become stronger and stronger. Finally, the movement of the electrons will be dynamically balanced, and the inner electric field will also be fixed. Because the electronic movement is dynamically balanced, that is to say, the width of the Area clipped by the red line is fixed.

Note that all carriers in the space charge area are exhausted.

We call it the pn.