I, LED light-emitting structure and principle

50 years ago, people have been understanding of semiconductor materials can have a basic knowledge of light, the diodes produce the first commercial in 1960. LED is the English light emitting diode (LED) acronym, which is the basic structure of an electroluminescent semiconductor materials, put a lead on the shelf, and then surrounded by epoxy resin sealing, protect the internal core of the line Effect, so we have good seismic performance of the LED.

Light-emitting diode is the core of the p-n-type semiconductor and semiconductor chips formed in the p-type semiconductor and semiconductor-n there is a transition layer, known as the pn junction. In some of the PN junction semiconductor materials, into a small number of the carrier and the majority of the carrier when the complex will be redundant in the form of light energy to release in order to directly convert electrical energy into light energy. PN junction reverse voltage increases, the minority-carrier injection is difficult, it is not luminous. This use of injection-EL produced by the principle of diode called light-emitting diodes, commonly known as LED. When it forward in the work of state (that is, together with the two ends of forward voltage), current flows from the anode cathode LED, semiconductor crystals in respect of the issue from the ultraviolet to infrared light in different colors, light and the strength of the current relevant.

Second, LED light source characteristics

1. Voltage: LED using low-voltage power supply voltage in the 6-24V, based on the product vary, so it is a high-voltage power than the more secure power supply, in particular, apply to public places.

2. Performance: energy efficient than incandescent light with the reduction of 80%

3. Applicability: small, each LED unit is a small square of 3-5mm, it can be prepared into the shape of the device, and suitable for the volatile environment

4. Stability: 100,000 hours, light for the initial decline of 50%

5. Response time: the incandescent millisecond response time for the class, LED lights have a response time of nanosecond

6. On the environment: no harmful metal mercury

7. Color: current can change the color, light-emitting diodes easily modified by chemical methods, materials to adjust and band structure of the band gap, the realization of red, yellow, and green blue light-emitting multi-color orange. If the current time for the small red LED, as the current increases, in turn can become orange, yellow, green for the final

8. Price: LED price is more expensive than incandescent in, a few of the LED price can Incandescent with a considerable price, and each is usually required by the lights on the 300 to 500 constitutes a diode.

Third, the type of monochromatic LED and its development history

Application of the first principles of light-emitting semiconductor PN junction of the LED light source made available in the early 1960s. At that time, the use of building materials is GaAsP, red hair (λp = 650nm), in the drive current of 20 milliamperes flux that only a few parts per thousand lumens, the luminous efficiency of about 0.1 lm / watt.

In the mid-70, and In the introduction of elements N, so that the LED have a green light (λp = 555nm), yellow (λp = 590nm) and orange light (λp = 610nm), luminous efficiency has increased to 1 lumen / watt.

By the early 1980s, there have been GaAlAs the LED light source, making the red LED light efficiency of 10 lumens / watt.

In the early 1990s, red hair, yellow hair and GaAlInP of green, blue GaInN of two successful development of new materials, so that the LED light has been significantly improved efficiency. In 2000, which caused the LED in red, orange zone (λp = 615nm) optical efficiency of 100 lm / W, which made the green LED in the region (λp = 530nm) light efficiency can reach 50 lm / Watts.

Fourth, the application of monochromatic LED

Initially used as instruments of the LED light source direction, then all kinds of light-colored LED traffic lights in the display area and widely used, have had a very good economic and social benefits. The 12-inch red traffic lights, for example, in the United States have been adopted long-life, low efficiency of light as a 140-watt incandescent light sources, which produce 2000 lumens of white light. By the red filter, the loss of 90% of the light, leaving only 200 lumens of red light. In the light of the new design, Lumileds has used a 18 red LED light source, including the loss of the circuit, a total power consumption of 14 watts, can produce the same luminous efficiency.

Automotive LED light source is an important area of application. In 1987, my car started to install high brake lights, LED due to the fast response (nanosecond) can be followed as soon as possible so that drivers know the traffic situation and reduce rear-end accidents.

In addition, LED outdoor lights in the red, green, blue full-color screen, mini-flashlight key chain, and other fields have been applied.

Fifth, the development of white LED

For general lighting, people need more white light source. In 1998 made the successful development of white LED's. This is the LED chip and GaN Yttrium Aluminum Garnet (YAG) package together made. GaN blue chip fat (λp = 465nm, Wd = 30nm), high-temperature sintering made of Ce3 + with the YAG phosphor excited by this ray of yellow light after the launch, the peak 550nm. Blu-ray-based LED chip installed in the bowl reflector cavity, covered with a mixture of YAG thin layer of resin, about 200-500nm. LED substrates issued by the phosphor was part of the Blu-ray absorption, and the other part of the Blu-ray phosphors and issued by the mixed yellow, white light can be obtained. Now, for InGaN / YAG white LED, by changing the YAG phosphor and adjusting the chemical composition of the phosphor layer, the color temperature will be 3500-10000K of the white colored.

Reference link: http://www.17led.com/LEDdisplay/2008-03/32.html