Something about Intrinsic and Extrinsic Semiconductors

Something about Intrinsic and Extrinsic Semiconductors

There are three basic types of semiconductor materials: intrinsic semiconductors, extrinsic semiconductors, also known as impurity semiconductors. Both types of semiconductor materials can be supplied by PAM-XIAMEN.

1. What Is Intrinsic Semiconductor?

Intrinsic semiconductor refers to a pure semiconductor that is completely free of impurities and lattice defects, and generally such a semiconductor whose electrical conductivity is mainly determined by the intrinsic excitation of the material. Its internal electron and hole concentrations are equal. Silicon (Si), germanium (Ge), and gallium arsenide (GaAs) are the typical intrinsic semiconductor materials. We can grow Intrinsic SiC Epilayer on silicon carbide substrate.

2. What Is Extrinsic Semiconductor?

Doping certain trace elements as impurities in intrinsic semiconductors can significantly change the conductivity of semiconductors. The impurities incorporated are mainly trivalent or pentavalent elements. Intrinsic semiconductors doped with impurities are called extrinsic semiconductors. In the preparation of extrinsic semiconductors, the intrinsic semiconductors are generally doped in proportions of the order of one millionth.

Intrinsic semiconductors have weak electrical conductivity and poor thermal stability, so it is not suitable to directly use them to manufacture semiconductor devices. Most semiconductor devices are made of semiconductors containing a certain amount of certain impurities. According to the different properties of doping impurities, impurity semiconductors are divided into N-type semiconductors and P-type semiconductors.

2.1 N-Type Semiconductor

Intrinsic semiconductor silicon (or germanium) is doped with a small amount of 5-valent elements, such as phosphorus, and phosphorus atoms replace a small amount of silicon atoms in the silicon crystal, occupying certain positions on the lattice. It can be seen from the figure that the outermost layer of phosphorus atom has 5 valence electrons. Among them, 4 valence electrons form a covalent bond structure with the adjacent 4 silicon atoms respectively, and the extra valence electron is outside the covalent bond and is only weakly bound by the phosphorus. Therefore, at room temperature, the energy needed to break free can be obtained and become free electrons, which are free between the lattices. Phosphorus atoms that lose electrons become immobile positive ions. Phosphorus atoms are called donor atoms because they can release one electron, also known as donor impurities.

N type silicon

In an intrinsic semiconductor, one free electron can be generated for each phosphorus atom doped, while the number of holes generated by intrinsic excitation remains unchanged. In this way, in the semiconductor doped with phosphorus, the number of free electrons far exceeds the number of holes, becoming the majority carrier (referred to as the majority), and the hole is the minority carrier (referred to as the minority). Obviously, electrons are mainly involved in conduction, so this kind of semiconductor is called electron-type semiconductor, or N-type semiconductor for short. Take our 4H N Type SiC Substrate for example.

2.2 P-Type Semiconductor

In the intrinsic semiconductor silicon (or germanium), if a trace amount of trivalent elements, such as boron, is doped, then the boron atoms replace a small amount of silicon atoms in the crystal and occupy certain positions on the lattice. It can be seen from the figure that the 3 valence electrons of the boron atom respectively form a complete covalent bond with the 3 valence electrons in the adjacent 3 silicon atoms, while the covalent bond of the other adjacent silicon atom lacks 1 electron and 1 hole. After this hole is filled with valence electrons from nearby silicon atoms, the trivalent boron atom gains one electron and becomes a negative ion. At the same time, a hole appears on the adjacent covalent bond. Since boron atoms play the role of accepting electrons, they are called acceptor atoms, also known as acceptor impurities.

P type silicon

One hole can be provided for every boron atom doped in an intrinsic semiconductor. When a certain number of boron atoms are doped, the number of holes in the semiconductor can be much larger than the number of intrinsically excited electrons, becoming the majority carrier, and the electrons becoming minority carriers. Obviously, it is mainly holes that participate in conduction, so this semiconductor is called a hole-type semiconductor, or P-type semiconductor for short. More p-type semiconductor of PAM-XIAMEN, please refer to the GaN Epitaxial Growth on Sapphire for LED.

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