Persistence and Amalgamation Types in the Electronic Structure of Mixed Crystals

The intrinsic optical spectra of substitutional binary solid solutions can be classified into two types, persistence and amalgamation types. In the former, two structures corresponding to the two constituent substances do persist. In the latter, they are amalgamated in a single one. A unifying theoretical expression is obtained by which both the persistence and the amalgamation types can be described. Numerical results based on that expression are given assuming a simple form for the state density of the band. On the basis of them, various situations realized in mixed crystals are discussed in the light of the experimental information, with particular emphasis on the behavior of the optical spectra with the change in composition.