 | ||
One of the most studied atomic ordering is CuPt type ordering in III-V semiconductor alloy. It occurs in III-V alloy when the cation planes take an alternate sequence of A-rich and B-rich plane following AxB1−xC. The resulting structure is usually called as superlattice-like structure along [1-11] or [-111] – called (111) B plane, or along [-1-1-1] or [11-1] – called (111) A plane. The two ordering direction is thus called CuPt type A and B ordering.
The same type ordering is also observed in II-VI alloy such as CdZnTe alloy. The ordering sequence viewed on atomic planes along [-111] and [1-11] reveals Cd and Zn alternating planes. Figure 1 below shows schematically the ordering mentioned:
Figure 1. Example of Cu-Pt type ordering in CdZnTe alloy
(figures courtesy of Journal of Materials Science Letters 22, 2003, 1263–1267)
This ordering reduces the lattice symmetry ordering to L11 and leads to change of its optical and electrical properties. The apparent effects are: band gap reduction, valence band splitting, and optical anisotropy. For instance, in CuPt type B ordering, the L point of the Brillouin zone fold back to the Γ-point, and the folded band “repels” the original conduction band minimum and bring down the bottom of conduction band.