The basic principle of LED display light emitting diode (LED) is a photoelectric component made of 35 compound semiconductors, and its core is PN junction. Under positive voltage, electrons are injected into the P region from the N region, and the holes are injected into the N region from the P region. Some of the minority carriers in the other side are combined with most of the carriers. The properties of the material forming the PN junction (the band gap) determine the wavelength of the light, which determines the color of the light for the visible light. The main features of LED are: small volume, low power consumption, long service life, high brightness and low calorie, environmental protection and durable and so on. Working at an appropriate current and voltage, the service life of LED can be as long as 100 thousand hours. The classification and application of LED based on the type of light emitted by LED can be divided into two kinds: visible light LED and invisible light LED. The visible light LED includes red, orange, yellow, green, blue and purple LED. The red light LED material is mainly GaP (two elements), AlGaAs (three element system) and AlGaInP (four system), and blue / white light LED is dominated by GaN. The application of LED is very wide, mainly including:
1, LED display: indoor and outdoor billboard, sports scoreboard, information display and so on;
2, signal light: the city traffic signal lights, expressway, railway and airport signal lights in the big and middle cities of the country, and the function instructions of electronic equipment;
3, light color lighting: outdoor landscape lighting and indoor decoration lighting;
4, special purpose lighting: portable lighting (flashlight, headlamp), low illumination (corridor lamp, door lamp, court lamp), reading lights (airplane, train, car reading lamp), microscope lamp, camera flash, desk lamp and street lamp.
5, safety lighting: mine lamp, explosion-proof lamp, emergency lamp, safety indicator lamp;
6, backlight: liquid crystal display, LCD TV backlight.
In 7, including: automobile lamp lighting and vehicle lighting inside the car, the car dashboard, including Denso products (light switch, audio and so on), switch back light, reading lamp and external brake lights, taillights, side lights and headlights.
8, other applications: consumption, such as children''s flash shoes, Christmas tree LED lights and so on.
The entry threshold of the LED industry chain is gradually reduced from the upstream to downstream industry. The upstream is single crystal and its epitaxy, the middle reaches is processed by LED chip, and the downstream is package test and application. Among them, the upper and middle reaches are high in technology and large in capital investment, which is the most competitive and risk management field in the international competition. In the LED industry chain, LED epitaxial films and chips account for about 70% of the industry''s profits, LED packaging accounts for about 10~20%, and LED applications may also account for 10~20%. The single crystal is the substrate for the manufacture of LED, also known as the substrate, with sapphire, silicon carbide, GaAs and GaP as materials. The epitaxial films are single crystal films with different layers of thickness on single crystal, such as AlGaAs, AlGaInP, GaInN and so on, which can be used to achieve different colors or wavelengths of LED. The common epitaxy methods include liquid phase epitaxy (LPE), vapor phase epitaxy (VPE) and metal organic chemical vapor deposition (MOCVD). VPE and LPE technologies are quite mature and can be used to grow the general brightness LED. The MOCVD method must be used for the growth of high brightness LED. At present, the main manufacturers of MOVCD in the world are Germany''s AIXTRON company and American VEECO company. The former accounts for about 60%~70%''s international market share, and the latter occupies 30%~40%. The equipment produced by Japanese manufacturers is basically limited to domestic sales in Japan. The middle reaches are mainly chip design and processing. According to the performance requirements of LED, the middle reaches manufacturers carry out the device structure and process design, through the epitaxial wafer diffusion, then metal coating, then lithography, heat treatment, forming metal electrodes, then the substrate is thin and polished and then cut. The downstream includes the encapsulation test and application of LED chip. LED encapsulation refers to connecting the outer lead to the electrode of the LED chip to form a LED device, which encapsulates the role of protecting the LED chip and improving the efficiency of the optical extraction. LED packaging technology is developed on the basis of encapsulation technology of semiconductor discrete devices. At present, the main packaging types of LED products are Lamp, ThroughHole, surface installation (SMD), direct bonding (DirectBonding) and so on. The SMD type LED volume is smaller than that of other traditional LED, so the SMD type is mainly used for the backlight of the mobile phone screen and the mobile phone key, which is greatly influenced by the demand of the mobile phone.