1. Semiconductors
Insulators and conductors are familiar things. A semiconductor is one whose electrical conductivity is lower than that of a conductor and higher than that of an insulator. In essence, the electrical conductivity of the substance depends on the atomic structure, the outermost electron of the atom is easy to break free of the bondage of the nucleus to become a free electron (conductor), the outermost electron is difficult to break free of the bondage (insulator), between the two is the semiconductor.
2. Intrinsic semiconductors
After a certain process to make a semiconductor into a structure with a very regular atomic structure is an intrinsic semiconductor. In this neatly arranged atomic structure, each nucleus is surrounded by an outer layer of electrons. Atoms are also neatly next to each other. Atoms share electrons, which is called a covalent bond.
If this covalent bond breaks free, it becomes a free electron. Then the position of the original k covalent bond is empty, called a hole. The free electrons are charged, and at the same time the original structure of the atom was the balance between the nucleus and the external electrons, and now the covalent bond is broken, the balance is broken, so the hole is also charged.
If a power plant is added to both ends of the intrinsic semiconductor, the free electrons will move in a directional direction, and the holes in this direction will be filled by the free electrons moving in. If the free electrons are used as a reference point, the holes can also be considered to move in the opposite direction. The charge polarity of the free electron and the hole is opposite, so the current in an intrinsic semiconductor is the sum of the two currents.
3. Impurity semiconductor
When an impurity is added to an intrinsic semiconductor, it becomes an impurity semiconductor. Depending on the impurities involved, the semiconductor is divided into N-type semiconductors and P-type semiconductors.
Take a semiconductor made of silicon as an example. Silicon atom is essentially a quadrivalent element, if the inclusion of the pentavalent element becomes an N-type semiconductor, the inclusion of the trivalent element becomes a P-type semiconductor. N-type semiconductors, because of the inclusion of pentavalent elements, that is, there are five electrons on the outside of a nucleus. Silicon has only four electrons outside its core, which is one more electron than silicon. Then the free electrons are the majority carriers of most N-type semiconductors. The same P-type semiconductor includes a trivalent element, which has one less electron than silicon, and y is one more hole. Then most of the carriers in P-type semiconductors are holes.
Both P-type and N-type semiconductors have stronger electrical conductivity than in the past.
4.PN knot
If through a special process, one half of a silicon wafer is made into a P-type semiconductor and the other half into an N-type semiconductor. Then the interface between P-type semiconductor and N-type semiconductor is the PN junction.
As mentioned above, N-type semiconductors are formed by adding a pentavalent element to an intrinsic semiconductor, and P-type semiconductors are formed by adding a trivalent element to an intrinsic semiconductor. That is to say, N-type semiconductors have many more free electrons (most charge carriers), and P-type semiconductors have many more holes (most charge carriers). So at this point, half of the silicon has a lot more free electrons, and half of the silicon has a lot more holes. Matter always moves from a place of high concentration to a place of low concentration (diffusion motion). The free electrons in N-region must
When the hole in the P region is diffused, the hole in the opposite P region will also diffuse to the N region, which leads to the combination of the hole and the free electron, so the concentration of most carriers near the interface will decrease. After a long time
Diffusion movement, PN junction will reach dynamic equilibrium, but if the PN junction at both ends of the voltage is added, this balance will be destroyed, the type of applied voltage is different, PN junction shows a completely different electrical conductivity (cause, P
Most carriers in the N region are different, if the voltage is reversed, the lack of itself, but also sent to the other side, the other side is exactly the least lack of this east, think). Therefore, the PN junction exhibits unidirectional conductivity.