LED (Light Emitting Diode), a solid-state semiconductor device that converts electricity directly into light. The heart of the LED is a semiconductor wafer. One end of the wafer is attached to a holder, one end is the negative pole, and the other end is connected to the positive pole of the power supply, so that the entire wafer is encapsulated by epoxy resin.
The semiconductor wafer consists of two parts, one part is a P-type semiconductor, in which the hole dominates, and the other end is an N-type semiconductor, which is mainly electrons here. But when the two semiconductors are connected, they form a PN junction. When a current is applied to the wafer through the wire, the electrons are pushed toward the P region. In the P region, electrons recombine with the holes, and then the energy is emitted in the form of photons. This is the principle of LED illumination. The wavelength of light, which is the color of light, is determined by the material that forms the PN junction. Because the LED lamp does not generate heat, the electric energy is converted into light energy as much as possible, and the ordinary lamp converts a lot of electric energy into heat energy due to the heat generation, which is wasted. In contrast, LED lighting is energy efficient.
Fifty years ago, people learned about the basics of semiconductor materials that produced light. The first commercial diode was born in 1960. LED is the abbreviation of English light emitting diode. Its basic structure is an electroluminescent semiconductor material placed on a leaded shelf and then sealed with epoxy resin to protect the inner core. The role, so the LED's seismic performance is good.
The core of the LED is a wafer consisting of a p-type semiconductor and an n-type semiconductor. There is a transition layer between the p-type semiconductor and the n-type semiconductor, called a pn junction. In some PN junctions of semiconductor materials, the injected minority carriers recombine with the majority carriers to release excess energy in the form of light, thereby directly converting electrical energy into light energy. The PN junction adds a reverse voltage, and minority carriers are difficult to inject, so they do not emit light. Such a diode fabricated by the principle of injection electroluminescence is called a light-emitting diode, and is generally called an LED. When it is in the forward working state (ie, the forward voltage is applied to both ends), when the current flows from the anode of the LED to the cathode, the semiconductor crystal emits light of different colors from ultraviolet to infrared, and the intensity of the light is related to the current.
Originally used as an indicator light source for instrumentation, LEDs of various light colors have been widely used in traffic lights and large-area displays, resulting in good economic and social benefits. Take the 12-inch red traffic light as an example. In the United States, a long-life, low-efficiency 140-watt incandescent lamp was used as the light source, which produced 2000 lumens of white light. After passing the red filter, the light loss is 90%, leaving only 200 lumens of red light. In the newly designed lamp, Lumileds used 18 red LED light sources, including circuit losses, to consume 14 watts of electricity, which can produce the same light effect. Automotive signal lights are also an important area for LED light source applications.
For general lighting, people need a white light source. In 1998, white LEDs were successfully developed. This LED is made by encapsulating a GaN chip and yttrium aluminum garnet (YAG). The GaN chip emits blue light (Î»p=465 nm, Wd=30 nm), and the Ce3+-containing YAG phosphor prepared by high-temperature sintering is excited by the blue light to emit a yellow light with a peak of 550 nm. The blue LED substrate is mounted in a bowl-shaped reflective cavity covered with a thin layer of resin mixed with YAG, about 200-500 nm. The blue portion of the LED substrate is absorbed by the phosphor, and the other portion of the blue light is mixed with the yellow light emitted by the phosphor to obtain white light. Now, for InGaN/YAG white LEDs, by changing the chemical composition of the YAG phosphor and adjusting the thickness of the phosphor layer, white light of various colors having a color temperature of 3500 to 10000K can be obtained. The method of obtaining white light by a blue LED is simple in structure, low in cost, and high in technology maturity, so it is most used.
In the 1960s, scientists and technicians used the principle of semiconductor PN junction light to develop LED light-emitting diodes. The LED used at that time was made of GaASP, and its color was red. After nearly 30 years of development, the LEDs that everyone is familiar with now can emit red, orange, yellow, green, blue and other colors. However, the white LEDs required for lighting have only been developed in recent years. Here, readers are introduced to white LEDs for lighting.
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