Gallium arsenide (GaAs) is a chemical compound composed of gallium and arsenic. It is an important semiconductor, and is used to make devices such as microwave frequency integrated circuits, infrared light-emitting diodes and laser diodes. The electronic properties of GaAs are superior to silicon's. It has a higher saturated electron velocity and higher electron mobility, allowing it to function at frequencies in excess of 250 GHz. Also, GaAs devices generate less noise than silicon devices. .
Another advantage of GaAs is that it has a direct bandgap. This means that it can be used to emit light. Silicon has an indirect bandgap, and so is very poor at emitting light. Nonetheless, recent advances may make silicon LEDs and lasers possible. Silicon has two major advantages over GaAs. First, silicon is cheap. This is for several reasons: silicon's large wafer size (maximum of ~300mm compared to ~150mm diameter), high strength allowing for easier processing, and of course the scale of the economy. .
The second major advantage is the existence of silicon dioxide "one of the best known insulators of any kind. Silicon dioxide can easily be incorporated into silicon circuits wherever a good insulator is required. GaAs circuits must either use the intrinsic semiconductor itself or silicon nitride; neither comes close to the extremely good properties of silicon dioxide. .
Gallium arsenide integrated circuits are commonly used in mobile phones, satellite communications, microwave point-to-point links, and some radar systems. Cray Research attempted to make a GaAs-based supercomputer in the early 1990s. The venture failed, and the company filed for bankruptcy in 1995. The major challenge in making gallium arsenide MOSFETs is perfecting the thin gate oxide material that's directly below the transistor's gate electrode, which receives electrical signal and acts as the transistor's switch by turning it on and off.
(Hennessey Interview) As Kevin Hennessey explains, he works with epitaxlly grown Gallium Arsenide with Indium quantum dots. He takes a substrate wafer of Gallium Arsenide and in a chamber there are connected MBE heads which are controlled to emit different elements. ...
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Over the past several years, temperatures around the world kept rising. Sometimes it's unbearable for people on this planet. "The temperature during an eight-day heat wave in Chicago in July 1995 hovered around 100 degrees Fahrenheit. High levels of humidity made the air feel even hotter, creating an almost unbearable and, ultimately, fatal environment. 556 number of deaths was attributed to the heat, which struck the elderly" ("Issues and Controversies: Global Warming "). Until human populations soared and began burning fossil fuels, greenhouse gases remained in relative balance. ...
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