Electronic Structures of a Quantum Well of Alloy Semiconductor

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We have theoretically studied electyronic and optical properties of a quantum well (QW) in which the well region is constructed from a binary alloy semiconductor A_<1-x>B_x in the coherent potential approximation (CPA). A tight binding model is used for a single particle (electron, hole, Frenkel exciton) in the well composed by a rectangular array of N_xxN_yxN_z sites. The effect of the diagonal randomness is reduced to the coherent potential S(E), which is assumed to be the same for all sites, and is selfconsistently determined with the average Green's function. For a slab (∞, ∞, N_z) and wire (∞, N_y, N_z), the density of states ρ(E) is composed of N_z (or N_yxN_z) subbands, each shows the two (one)-dimensional van-Hove singularity. When x (or 1-x) is small, a B (A) impurity-band always appears at the lower (higher) energy side of the lowest (highest) host-band. As the well width becomes narrower and/or the dimensionality decreases, the boundary for Δ/t decreases which separates the amalgamation type and the persistence type. The results have been published in the Proceeding of MRS 2000 Fall symposium G "GaN and Related Alloys" 639 (2001) and Phys. Stat. Sol. (b), 229.