Photonics is a term sometimes used interchangeably with "opto" which is short for "optical" and used especially when combining light-related devices with electronics, thus you'll often hear or see "optoelectronics." But "photonics" is the more valid and eclectic term. Photonics is defined by Photonics Spectra magazine in their masthead as, "the technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The range of applications of photonics extends from energy generation to detection to communications and information processing." Since it is an area where silicon cannot adequately compete, photonics, which includes the all-optical networks driving today's broadband applications, is where the compound semiconductor clearly shine. Whereas silicon can only do silicon, there are are world of different kinds and types of compound semiconductor materials and devices. As the silicon semiconductor industry runs up against its physical limits, it turns to the compound semiconductor industry for next generation devices and integrated solutions. Although compound semiconductors have been actively on the scene for about 30 years, the field is only now becoming popular. It's a bit like being the classic "20 year overnight success" story, and all newcomers to the field are heartily welcome.

The various elements that are combined to become compound semiconductors can be found in any Periodic Table of Elements. The most common material combinations used in compound semiconductor technology come from the Group III and Group V materials, although II-VIs and some from the Group IVs are also growing in popularity as applications become more real and widespread. The most popular of the compounds are Gallium (Ga) and Arsenic (As) and referred to as Gallium Arsenide or GaAs and pronounced 'gas.' Indium (In) and Phosphorus (P) make Indium Phosphide or InP (no easy nickname) and Silicon (Si) and Carbon (C) make Silicon Carbide or SiC (also no nickname). Gallium and various Nitrogen elements make Gallium Nitride, or GaN which is simply pronounced as 'gan.' Often, more than two elements are combined, with Aluminum (Al) included in the mixture to make alloys which take on exotic or complicated sounding combinations such as InGaP (in-gap), AlGaP (al-gap) and AlGaN (al-gan). No matter how they are pronounced, all combinations are tremendously exciting, and when properly prepared for device manufacturing, they can perform feats previously thought impossible.

Like silicon, compound semiconductor starting material is "pulled" from equipment called "crystal pullers" into boules of bulk crystals, using a starting seed that grows the boule larger and larger depending on the state of the art of that particular material science. Whereas silicon bulk substrates are available in 8 inch and even 13 inches in diameter due to the maturity of that technology, GaAs is at 6 inch, InP at 2-4 inch and SiC at 3 inch. From those starting boules, wafers are sliced and polished. Some wafers are clear, some brightly colored and most look like silicon and are very thin and bright, shiny silver. Most all of them are brittle. Breakage and defects within the boule or wafer continue to threaten yields. Even silicon isn't defect free, but all the compounds have a long way to go before they are as consistently reliable as silicon. GaAs is the furthest along, thus the most defect-free. InP and SiC are the next most mature, with Mercury (Hg) Cadmium (Cd) Tellurium (Te) (also known as "MCT" or "mer-cad-tel" ) and GaN only available as mere chunks and difficult to obtain. However... the components that can be designed from a mere piece of those little "chunks" of MCT or GaN are absolutely incredible and literally extend the human senses beyond belief! Whatever the size, shape or color, the boules and resulting wafers can be semi-insulating or semi-conducting, although all are referred to as semiconductor materials. (The semiconductor business and compounds in particular are fully of exceptions, often using somewhat misleading terminology). Whether silicon or compound semiconductors, the wafers are always sliced and polished to form the thin starting substrates on which the ultimate electronic or photonic devices are etched or grown.

Device processing takes one of two primary routes. The most mature process is GaAs MESFET which is similar to silicon's CMOS or CMOS processing and is done with the wafer going through a variety of etching and mask steps, ballroom style, within a clean room environment full of humans in clean room attire lovingly called "bunny suits" moving themselves and the wafers from station to station until the processing is complete. One of the reasons the compound semiconductors have taken giant strides in development and popularity is due to advancements in a process called epitaxy which is required to grow heterostructures such as HBTs and HEMTs. All of these are types of transistors. Unlike the human-intense "ballroom style" processing, compound semiconductor epitaxial processing takes place in reactors, or production platforms, that do not require as many humans nor their stations or floorspace. Epitaxy platforms are becoming progressively more robotic in nature, and considering the toxicity of the materials used and expense and space required for ballroom production, that makes profound sense. A high volume MOCVD production unit, for example, can work 24 hours a day, 7 days a week, without complaining or requiring a paycheck. In general, one individual production platform costs about $1 million. In manufacturing environments such as exist in Taiwan, where HB-LED are being produced like jelly beans, strings of 10 or more of these machines are working continuously with relatively few humans, and sharing vats of starting gases and solids that are used to grow the devices, atomic layer by atomic layer. From there, again like silicon, the individual devices are carefully tested, separated and packaged for insertion into an electronic or photonic system such as a cellphone, networking systems, or integrated into systems requiring high brightness (HB) LEDs or laser diodes (LDs), or the multijunction solar cells that keep a satellite functioning.