Semiconductor foundation of binary realization principle

Conductivity of objects

Under normal circumstances , We use a multimeter to measure the voltage or current of a section of wire , Its value is 0. The reason is the free electrons inside , At this time, there is no directional movement under the influence of electric field force . Pictured .

When the positive and negative poles of the power supply are added to both ends of the metal , here , Two sections of the wire generate an electric field , Free electrons flow from the negative pole of the electric field to the positive pole , We define the direction opposite to the moving direction of free electrons as the direction of current . At this time, an electric current is generated in the wire .

Atomic composition

We know , Free electrons are negatively charged , In the absence of electric field force , The wire is dead , That is, it will not emit electrons . The following figure is impossible .
[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-SHCCOoRH-1644932988536)(./images/ultraman.png)]
The reason why it is not charged is that there is an equivalent positive charge corresponding to it .
According to the knowledge of junior high school chemistry , An atom is composed of nuclei and extra nuclear electrons , The composition law is ：
Geometrically , The positive charge in the nucleus is a point , The name is proton .
And the electrons outside the nucleus move irregularly around the nucleus , Each layer is at most 2n^{2 One electron . The outermost layer does not exceed 8 One electron . This is what junior high school textbooks say 2,8,8 structure}

Why is water stable

With the above knowledge , Let's talk about a special substance —— water .
Water is very stable , Junior high school physics tells us , The specific heat capacity of water is the largest , That is to say, water absorbs the most heat , This is why our car has a water tank to cool the engine .
This means that water can absorb a lot of energy , But the nature is not easy to change .
Another example is that pure water can only generate hydrogen and oxygen after electrolysis , On the other hand, it also proves that only by forcibly injecting water with energy can water molecules change .
Why can water be so stable , The reason is that in the molecular structure of water , The constraint between protons and extranuclear electrons is covalent bond .

That is, the extranuclear electron of the hydrogen atom and an extranuclear electron of the oxygen atom form together . So it looks like , There are 2 One electron , Outside the nucleus of oxygen atom 4 One electron , Combined with the above-mentioned law of the number of extranuclear electrons , This structure is super stable .

IVA Representatives of the clan —— carbon

Next , Let's look at a common substance —— carbon （Carbon）, Carbon is also covalent . It's just , The number of electrons outside the core of carbon itself is 4 individual , If one carbon atom is surrounded by other carbon atoms , Then the number of electrons outside the nucleus can be formed 8 Structure , It is also very stable . for example , Ink with carbon as the main component can preserve calligraphy and painting works for thousands of years , The hardness of diamond is so high that it can cut the glass .

Again , On the periodic table , All substances of this family have this property , Because the number of electrons outside the nucleus is 4.

Formation and classification of semiconductors

Dear friends , See no , stay IVA In the family , Silicon is on it , Germanium is also on it , We often hear the news about the silicon chip used on the chip , Silicon tube , Germanium tubes are because they have covalent bonds , Very stable . Since it is very stable , It should be like water , Non conductive （ Pure water does not conduct electricity , Generally speaking, water conducts electricity because the tap water we usually use is a mixture , There are ions in it ）. Why are these substances used in the applications of computer and other electronic industries , This leads to the following topic —— semiconductor .

P Type semiconductor

Suppose silicon is used as the main material , Doping some trivalent elements in the middle （ For example, boron ）, Then the molecular composition will be as shown in the figure below .

You can see , The original covalent bond will be solved , One of the positions is reserved for a hole , This type of substance is called P Type semiconductor .
If an electric field is applied to both sides of this substance , Immediately, electrons flow in from the side , Fill this vacancy , Form conductivity .
stay P In a semiconductor , The hole is multiparticle , Free electrons are minority electrons , It mainly depends on hole conduction .
because P The amount of positive charge is equal to the amount of negative charge in type a semiconductor , so P Type a semiconductor is electrically neutral . Holes are mainly provided by impurity atoms , Free electrons are formed by thermal excitation .

N Type semiconductor

Suppose silicon is used as the main material , Doping some pentavalent elements in the middle （ For example, phosphorus ）, Then the molecular composition will be as shown in the figure below .

You can see , There is an extra electron in one of the positions , This type of substance is called N Type semiconductor .
If an electric field is applied to both sides of this substance , That extra electron will move away after absorbing energy , Form conductivity .
because N The amount of positive charge is equal to the amount of negative charge in type a semiconductor , so N Type a semiconductor is electrically neutral . Free electrons are mainly provided by impurity atoms , Holes are formed by thermal excitation . The more impurities are added , children （ Free electrons ） The higher the concentration of , The stronger the conductivity .