Basic knowledge of semiconductors

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Basic knowledge of semiconductors [Copy link]

Semiconductors with pure crystal structures are called intrinsic semiconductors . Commonly used semiconductor materials are silicon and germanium. They are both tetravalent elements, with four valence electrons in the outermost orbit of the atomic structure. When silicon or germanium is made into crystals, they are closely linked together by covalent bonds .
Some valence electrons in the covalent bond gain some energy due to thermal motion, thus breaking free from the constraints of the covalent bond and becoming free electrons, leaving vacancies on the covalent bond. We call these vacancies holes , which are positively charged. Let's use a crystal structure diagram to describe it; as shown in Figure (1): The dotted lines in the figure represent covalent bonds. Under the action of an external electric field, the free electrons move in a directional manner, forming an electronic current;
At the same time, valence electrons also fill holes in a certain direction at a time, causing the holes to move in a directional manner and forming a hole current.
Therefore, there are two types of carriers in the crystal, namely negatively charged free electrons and positively charged holes, which appear in pairs.
2. Impurity semiconductor
In an intrinsic semiconductor, the concentration of the two carriers is very low, so the conductivity is very poor. We controllably add specific impurities into the crystal to change its conductivity, and this semiconductor is called an impurity semiconductor .
1. N-type semiconductor
In intrinsic semiconductors, pentavalent elements are doped, so that some atoms in the crystal are replaced by impurity atoms. Because the outermost layer of the impurity atom has 5 valence electrons, it has an extra free electron after forming covalent bonds with the surrounding atoms, so the concentration of holes is much smaller than the concentration of free electrons. However, the product of the concentration of electrons and the concentration of holes is a constant, which has nothing to do with doping. In N-type semiconductors, free electrons are majority carriers, and holes are minority carriers.
2. P-type semiconductor
In intrinsic semiconductors, trivalent elements are doped, and some atoms in the crystal are replaced by impurity atoms. However, the outermost layer of the impurity atom has only three valence electrons. After it forms covalent bonds with the surrounding atoms, there is still an extra hole, so the concentration of holes is much greater than the concentration of free electrons. In P-type semiconductors, free electrons are minority carriers, and holes are majority carriers.