The Basics Behind High Brightness LEDs
Source/Type: Reference Materials

April 4, 2001... High Brightness (HB) and Ultra High Brightness (UHB) Light Emitting Diodes (LEDs) are quickly replacing conventional lighting in a wide variety of applications. By obvious definition, they are distinguishable from conventional, or common LEDs by their brightness levels. Whereas conventional LEDs have been in use for many years as simple indicator lights on TV sets, appliances, in automobiles, computers, hotel entry doors, elevators, etc., HB-LEDs are relatively new to the world of illumination. Both conventional LEDs and HB-LEDs are compound semiconductor devices. Conventional LEDs are relatively easy to manufacture, but all HB-LEDs must be grown by sophisticated compound semiconductor epitaxial growth techniques, the most popular growth method being MOCVD. And the higher the brightness levels or those in the blue spectrum (which include blue, green, violet and ultraviolet... and the combination of techniques that produce white LEDs), the more the compound semiconductor devices are dependent on such high level epitaxial growth and production techniques. Another important basic point, is that their is relatively little difference between the manufacturing of a very bright LED and a dim laser diode (LD). The growth techniques become quite similar in an sophisticated epitaxial growth environment. For example, the growth of an HB-LED and a Vertical Cavity Surface Emitting Laser (VCSEL) is surprisingly similar. VCSELs are quickly replacing conventional surface emitting lasers and are becoming a critical component in broadband communication applications. VCSELs, HB-LEDs and LDs are illustrative of the type of compound semiconductor devices that are responsible for the optical, or photonic devices that are literally revolutionizing the semiconductor industry. Essentially, these components do what silicon-based devices cannot... especially when it comes to generating, gathering, optimizing, and transmitting light.

Red and yellow spectrum HB-LEDs have been in use as traffic signals, warning lights and in a variety of automotive applications for some time. They are distinguishable as an array of small red or yellow light points versus light produced by one conventional lamp covered and brightened by a reflecting mechanism. But even that is changing, as brightness levels increase. It will soon be difficult to distinguish a HB-LED from a conventional lamp except when it comes to assessing the amount of heat, or energy expanded. HB-LED are cool to the touch and require considerably less power to operate. And they last considerably longer. These popular HB-LEDs are grown epitaxially on sophisticated production platforms such as MOCVD and MBE. Various elements are combined into the compound semiconductors that produce the color desired. InGaAlP (indium+gallium+aluminum+phosphide) AlGaAs (aluminum+gallium+arsenide), etc. The exception is blue spectrum HB-LEDs, which require the growth of nitride materials on as compatible substrates as can be found (most commonly, sapphire, silicon carbide, or aluminum nitride as large area nitride bulk substrates are not yet available). Gallium Nitride (GaN) is an amazing material of huge future potential, and is the underlying material science required to obtain blue spectrum HB-LEDs or laser diodes (LDs). As blue spectrum LEDs and LDs become perfected, the entire world of lighting as we know it will be expanded, improved, and made more efficient. This will ultimately represent a tremendous saving of global energy-requirements, thanks entirely to the world of compound semiconductor material science, development, and production. GaN is also under serious development as the means to achieving even more efficient electronic devices than either silicon or the more mature compounds can produce.

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