Electronic structure of random copolymers

The electronic structure of random copolymers (RCP) is theoretically investigated by the single-site coherent potential approximation. The results are also compared with those by the band calculation for the corresponding ordered system. In the A_{1 -x}B_x binary RCP, a strong reduction in the system band gap (E_g(A_1-xB_x)) is found in the dilute B region when the system has the relation of E_g(A)>E_g(B). This dependence is caused by the asymmetric quenching in the density-of-states (DOS) singularity at the band-edge states. The gap-opening mechanism and the asymmetric quenching are discussed by focusing on the role of the spatial dimension on the electronic structure of the random system, and the theoretical treatment is finally applied to the calculation of the joint DOS for the Si-Ge RCP system.