Approximation of excitonic absorption in disordered systems using a compositional-component-weighted coherent-potential approximation

Employing a recently developed technique of component-weighted two-particle Green's functions in the coherent-potential approximation (CPA) of a binary substitutional alloy A_cB1-c we extend the existing theory of excitons in such media using a contact potential model for the interaction between electrons and holes to an approximation which interpolates correctly between the limits of weak and strong disorder. With our approach we are also able to treat the case where the contact interaction between carriers varies between sites of different types, thus introducing further disorder into the system. Based on this approach we study numerically how the formation of exciton bound states changes as the strengths of the contact potentials associated with either of the two site types are varied through a large range of parameter values.