What Are Semiconductors
When electric current passes through various objects, different objects have different capacities to impede the flow of current. Some objects allow current to flow smoothly, while others do not allow it to pass or do so with certain resistance. This varying ability of objects to conduct electric current is called their conductivity. Different objects have different conductivity, with those having good conductivity being called conductors. Good conductors include silver, copper, aluminum, lead, tin, iron, mercury, carbon, and electrolytes. Conversely, objects with very poor conductivity are called insulators. Additionally, some objects have conductivity that is worse than conductors but better than insulators; these are called semiconductors. Common materials for transistors include silicon and germanium. CPUs in radios are also semiconductors.
Semiconductors have some special properties. For instance, the relationship between the resistance of semiconductors and temperature can be used to create thermosensitive components (thermistors) for automatic control; their light-sensitive properties can be used to create light-sensitive components for automatic control, such as solar cells, phototubes, and light-sensitive resistors.
One of the most important properties of semiconductors is that if trace impurities are appropriately doped into pure semiconductor materials, their conductivity can increase by millions of times. This characteristic allows for the manufacture of various semiconductor devices for different applications, such as semiconductor diodes and transistors.
By forming one side of a semiconductor into a P-type region and the other side into an N-type region, a thin layer with special properties is formed at the junction, commonly referred to as a PN junction. The upper part of the diagram shows the diffusion of charge carriers on either side of the P-type and N-type semiconductor interface (indicated by black arrows). The middle part illustrates the formation process of the PN junction, indicating that the diffusion of charge carriers is greater than the drift (indicated by blue arrows, while red arrows indicate the direction of the built-in electric field). The lower part shows the formation of the PN junction, representing the dynamic balance between diffusion and drift actions.
What Are the Uses of Semiconductors
Currently, widely used semiconductor materials include germanium, silicon, selenium, gallium arsenide, gallium phosphide, and indium antimonide, among which the production technology for germanium and silicon is more mature and more widely used.
Components and integrated circuits made from semiconductor materials are essential foundational products in the electronics industry and are extensively used in various aspects of electronic technology. The production and research of semiconductor materials, devices, and integrated circuits have become an important part of the electronics industry. Key areas for new product development and technology advancement include:
(1) Integrated Circuits
This is the most active area in semiconductor technology development, having advanced to the stage of large-scale integration. Tens of thousands of transistors can be fabricated on a silicon chip measuring just a few square millimeters, allowing for the creation of a microprocessor or the completion of other complex circuit functions on a single silicon chip. The development direction of integrated circuits is to achieve higher integration levels and lower power consumption while reaching microsecond-level information processing speeds.
(2) Microwave Devices
Semiconductor microwave devices include receivers, controllers, and transmitters. Receiver devices below the millimeter wave band are widely used. In the centimeter wave band, the power of transmitter devices has reached several watts, and efforts are being made to develop new devices and technologies to achieve higher output power.
(3) Optoelectronic Devices
The development of semiconductor light-emitting, imaging devices, and lasers has made optoelectronic devices an important field. Their applications mainly include: optical communication, digital displays, image reception, and optical integration.
What Are Semiconductors Made Of
Materials in nature can be classified based on their conductivity into conductors, insulators, and semiconductors. Semiconductor materials refer to a class of functional materials whose conductivity lies between conductive materials and insulating materials at room temperature. Conductivity is achieved through two types of charge carriers: electrons and holes, with resistivity generally ranging from 10-5 to 107 ohm·meters at room temperature. Typically, resistivity increases with temperature; however, doping with active impurities or using light or radiation can cause several orders of magnitude changes in resistivity. The silicon carbide detector was developed in 1906.
After the invention of the transistor in 1947, semiconductor materials have developed significantly as an independent material field and have become indispensable in the electronics industry and high-tech sectors. The conductivity of semiconductor materials is highly sensitive to certain trace impurities. High-purity semiconductor materials are called intrinsic semiconductors, which exhibit high resistivity at room temperature and are poor conductors of electricity. When appropriate impurities are doped into high-purity semiconductor materials, the resistivity is greatly reduced due to the conductive carriers provided by the impurity atoms. This type of doped semiconductor is commonly referred to as extrinsic semiconductors. Extrinsic semiconductors that conduct electricity through conduction band electrons are called N-type semiconductors, while those that conduct electricity through valence band holes are called P-type semiconductors.
When different types of semiconductors come into contact (forming a PN junction) or when semiconductors contact metals, diffusion occurs due to differences in electron (or hole) concentrations, forming a potential barrier at the contact point, resulting in unidirectional conductivity. Utilizing the unidirectional conductivity of PN junctions, various semiconductor devices can be manufactured, such as diodes, transistors, and thyristors.
Furthermore, the conductivity of semiconductor materials is highly sensitive to external conditions (such as heat, light, electricity, and magnetism), allowing for the manufacturing of various sensitive components for information conversion. The characteristic parameters of semiconductor materials include bandgap width, resistivity, carrier mobility, non-equilibrium carrier lifetime, and dislocation density. The bandgap width is determined by the electronic states and atomic configurations of the semiconductor and reflects the energy required for valence electrons of the atoms constituting the material to be excited from a bound state to a free state. Resistivity and carrier mobility reflect the conductive capacity of the material.
The non-equilibrium carrier lifetime reflects the relaxation characteristics of semiconductor materials as internal carriers transition from a non-equilibrium state to an equilibrium state under external influences (such as light or electric fields). Dislocations are the most common type of defect in crystals. Dislocation density is used to measure the degree of lattice integrity in single-crystal semiconductor materials, while this parameter does not apply to amorphous semiconductor materials. The characteristic parameters of semiconductor materials not only reflect the differences between semiconductor materials and other non-semiconductor materials but are also crucial in reflecting the variations in characteristics among various semiconductor materials, even the same material under different conditions.
Editor: Chen Zeman
Initial Review: Huang Mingming
Audit: Jin Xiangpeng
Audit Release: Jin Xiangpeng