# What is a boy? What does it have to do with minority carriers?

If you want to know what a minority carrier is, you must first know what a carrier is.
Conductors conduct electricity due to the movement of electrons, while semiconductor materials conduct electricity differently. In addition to electrons, there is also a type of hole that conducts electricity, and its conductivity depends on the concentration, distribution and mobility of both electrons and holes. These conductive electrons and holes are called carriers. It can be seen that the carrier is the carrier of the charge, that is, the charged particle that can move.

Due to the movement of the carriers, the electric current is generated. A substance with many carriers is a conductor. On the contrary, a substance with few or no carriers is an insulator, and a substance that can change the number of carriers is a semiconductor.

The number of electrons or holes per cubic centimeter is called the carrier concentration. The concentration of carriers is the main factor that determines the conductivity of semiconductors, and its unit is atoms/cm3. In an intrinsic semiconductor, the concentration of electrons and the concentration of holes are equal. Whereas in semiconductors containing impurities and lattice defects, the electron or hole concentrations are not equal.

We call carriers with a larger number as majority carriers, and carriers with a smaller number as minority carriers. For example, in an N-type semiconductor, electrons are the majority carriers and holes are the minority carriers, whereas in a P-type semiconductor, holes are the majority carriers and electrons are the minority carriers.

Minority carrier is short for minority carrier. Of course, the majority carrier can also be referred to as many.
When there is no electric field in the semiconductor, since the movement of electrons and holes in the lattice is irregular, the electrons and holes often collide with each other during the movement, that is, the electrons jump to the position of the holes, and the empty When the holes are filled, the electrons and holes disappear. This phenomenon is called the recombination of electrons and holes, that is, carrier recombination.

Electrons and holes continue to recombine, and at the same time, electrons and holes are continuously generated under the influence of temperature. If the temperature of the crystal remains unchanged, and there are no external light and electrical factors, then the number of recombined electrons and holes per unit time and the generation of The number of electrons and holes is equal, so the total carrier concentration of the crystal remains unchanged. This is called a state of equilibrium.

Under the external effect, as long as the external effect is conducive to the generation of electrons and holes, such as light irradiation, at this time, the generation rate of electrons and holes is greater than the recombination rate. The equilibrium state is disrupted, and the semiconductor appears with excess electrons and holes than the original concentration. These electrons and holes that are more than the equilibrium state are called non-equilibrium carriers. After the external effect disappears, the non-equilibrium carriers pass through the recombination action, and gradually disappear after a period of time. This gradual disappearance time is called the non-equilibrium carrier lifetime.

The so-called lifetime is the time that non-equilibrium carriers exist in the semiconductor.
In N-type semiconductors, when there are unbalanced electrons and holes, the electrons are unbalanced majority carriers and holes are unbalanced minority carriers; in P-type semiconductors, when unbalanced carriers appear, the opposite is true , holes are non-equilibrium majority carriers, and electrons are non-equilibrium minority carriers. The non-equilibrium minority carriers are generated and disappear through recombination (recombination with the majority carriers). The time of this process is the non-equilibrium minority carrier lifetime, referred to as the minority carrier lifetime, and its unit is μs (microseconds).

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