Concepts and Applications of Band Structure Engineering in Optoelectronics
The concept of electronic structure engineering is as old as semiconductor physics. Soon after the discovery of binary compound semiconductors such as GaP and GaAs it was realised that suitable solid mixtures of these materials could be used to alter the magnitude of the forbidden gap. The emergence of the optic cable provided a particularly strong impetus for such experimentation and as a result a new technology came into being of quaternary alloys involving elements of Ga, In, P, As etc. grown on high quality InP substrates (see, for example, Pearsall, 1982). Concurrently with the development of new alloys it has become possible to grow high quality epitaxial layers of technologically important semiconductors of almost arbitrary (and well controlled) thickness. In an alloy the band gap is changed by alterations of the alloy composition. There is a simple linear relationship between the alloy composition and band gap. A similar linear relation exists between the gap and the lattice constant. Semiconductor heterostructures offer a different way of achieving changes in band gap. When a thin layer of, say, GaAs is sandwiched between layers of Ga1−xAlxAs, the larger gap material (the alloy) acts as a simple potential barrier for electrons at the bottom of the conduction band of GaAs (e.g. Capasso and Margaritondo, 1988). The electron levels in GaAs are shifted as a result of the confining potential and their position with respect to the bulk band edges of GaAs can be estimated from the particle in a box model (Jaros, 1989).
KeywordsWave Function Conduction Band Minimum Atomic Potential Bulk Wave Band Offset
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