AIP Digital Archive
Semiconductor alloys like Hg1−xCdxTe and Al1−xGaxAs, where there is a close lattice constant match between the constituents, are nearly random. Consider mesoscopic size scales of radius r that are large compared with a lattice constant (∼25 A〈r〈∼250 A), but small compared with typical device dimensions. In such regions the number of substitutional sites is small enough so the root-mean-square concentration fluctuation 〈(Δx)2〉1/2 is sufficiently large to produce random arrays of mesoscopic "quantum dots" that adversely affect many device properties. The influence of the adverse effects differ among various properties—for example, electron and hole mobilities, lifetimes, and so on—but, in general, are worse the smaller the fundamental gap becomes. These kinds of fluctuations are suppressed in lattice-mismatched alloys like Hg1−xZnxTe and Ga1−xInxAs because there is a long-range strain energy penalty associated with them. Thus, lattice-mismatched alloys are more spatially uniform than lattice-matched alloys. © 1999 American Institute of Physics.
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