Alloys and Superlattices
In recent years, the concepts of band-gap engineering have become widespread especially for their impact on performance modifications of electron devices and for their suggestion of new methods of device operation. This has primarily arisen from the ability to modify material characteristics through alloying and through the use of superlattices and quantum wells to tune energy levels. If there is a single reason for the advent of alloys, it is the advantages that are offered by the tuning of the fundamental energy gaps (between conduction and valence bands) of the material system to some desired value. This single parameter governs the electrical and optical properties through the intrinsic carrier densities and the fundamental absorption edge. As the investigations of semiconductor materials has progressed, studies of the simple elements Si and Ge moved to the more interesting compounds of GaAs, AlAs, etc., and then to alloys of these compounds. Interestingly enough, the use of molecular-beam epitaxy has once again allowed interesting alloys of Si and Ge to be investigated.
KeywordsValence Band Band Structure Lower Conduction Band Random Alloy Virtual Crystal Approximation
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