The history of LED development
The discovery of semiconductor P-N junction luminescence can be traced back to the 1920s. French scientist O.W.Lossow first observed this luminescence phenomenon when he was studying SiC detectors. Due to the limitations of material preparation and device technology at that time, this important discovery was not quickly utilized. Until forty years later, with the progress of III-V group materials and device technology, people finally successfully developed a practical value GaAsP light-emitting diode emitting red light, which was mass-produced by GE as an instrument indicator. Since then, due to the further development of GaAs, Gap and other materials research and device technology, in addition to deep red LEDs, LED devices including orange, yellow, yellow-green and other colors have also emerged in the market in large numbers.
For various reasons, LED devices such as Gap and GaAsP have low luminous efficiency, and the light intensity is usually below 10mcd, which can only be used for indoor display purposes. Although the AlGaAs material enters the indirect jump-type region, the luminous efficiency drops rapidly. With the advancement of semiconductor materials and device technology, especially the growing maturity of epitaxial processes such as MOCVD, in the early 1990s, Nichia of Japan and Cree of the United States respectively used MOCVD technology in GaN-based LED epitaxial wafers with device structures were successfully grown on sapphire and SiC substrates, and blue, green and violet LED devices with high brightness were fabricated.
The emergence of ultra-high brightness LED devices has opened up extremely brilliant prospects for the expansion of LED application fields. The first is that the increase in brightness makes the application of LED devices move from indoors to outdoors. Even in strong sunlight, these cd-level LED tubes can still shine brightly and colorfully. At present, it has been widely used in outdoor large-screen display, vehicle status indication, traffic lights, LCD backlight and general lighting. The second feature of ultra-bright LEDs is the extension of the emission wavelength. The emergence of InGaAlP devices extends the emission band to the short-wave yellow-green region of 570 nm, while GaN-based devices further extend the emission wavelength to the green, blue, and violet bands. In this way, LED devices not only make WORLD colorful, but also make it possible to manufacture solid-state white lighting sources. Compared with conventional light sources, LED devices are cold light sources with long life and low power consumption. Secondly, LED devices also have the advantages of small size, sturdy and durable, low operating voltage, fast response, and easy connection with computers. Statistics show that in the last five years of the twentieth century, the application market of high-brightness LED products has maintained a growth rate of more than 40%. With the recovery of the WORLD economy and the start of the white lighting project, it is believed that the production and application of LED will usher in a greater climax.
