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AlGaAsAluminum Gallium Arsenide
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22 Science the researchers sandwiched a dense carpet of indium aluminum arsenide clusters between two layers of aluminum gallium arsenide. Each cluster had a diameter of about 20 nanometers, says study coauthor Simon Fafard.
Eaves and his colleagues obtained their results using a tunnel diode, in which electrons leak into a so-called quantum well consisting of a thin layer of gallium arsenide sandwiched between walls of aluminum gallium arsenide.
Known as a zone laser, this experimental device consists of several layers -- each 70 angstroms thick -- of indium gallium arsenide, gallium arsenide, and aluminum gallium arsenide. About 120 micrometers in diameter, this experimental laser produces infrared light.
Ashoori and his collaborators at AT&T Bell Laboratories in Murray Hill, N.J., create an artificial atom by sandwiching a thin layer of gallium arsenide between two layers of aluminum gallium arsenide. The artificial atom itself corresponds to a location - a few hundred angstroms wide - in the gallium arsenide crystal that can be completely emptied of electrons, then gradually refilled.
The researchers discovered they could make this smooth, hard oxide while studying the decade-long effects of exposure to air and moisture on aluminum gallium arsenide. In 1989, Holonyak and graduate student John M.
Constructed by putting metal "gates," or barriers, at the entrance and exit to a quantum dot fabricated at the boundary between layers of gallium arsenide and aluminum gallium arsenide, the device acts as a turnstile.
To elucidate the details of how such laser arrays function, the Sandia team used light pulses to activate microscopic lasing elements fabricated in semicongallium consisting of alternating layers of gallium aresenide and aluminum gallium arsenide. By chaning the area illuminated by the pulse, the researchers could activate different numbers of lasers in the array, then observe the beam emerging from the wafer surface.
The California scientists build even more intricate structures, called quantum-well-wire arrays, by using molecular beam epitaxy to lay down vertically and sometimes horizontally alternating layers of gallium arsenide and less conductive materials, in this case aluminum arsenide and aluminum gallium arsenide. By starting with a gallium-arsenide "staircase" crystal with atom-size steps, the researchers build up a "tilted superlattice" of the quantum-well wires (see micrograph).
Furthermore, when such electron waves pass through a carefully structured semiconductor superlattice made of extremely thin, alternating layers of gallium arsenide and aluminum gallium arsenide, the lattice acts like an energy filter, allowing only electrons with a certain energy through.
Morkoc's group has improved upon conventional MODFETs by sandwiching a 100-angstrom-thick layer of indium gallium arsenide (InGaAs) between the layers of aluminum gallium arsenide (AlGaAs) and gallium arsenide (GaAs) found in conventional devices.