DISORDER EFFECTS ON FREE-EXCITONS IN CDS1-XSEX MIXED-CRYSTALS

In CdS1−xSex mixed crystals the energies and transition probability ratios for free A, B, and C excitons are obtained as a function of the composition x by reflection and emission measurements at 77 K. The observation of the disorder‐allowed A(Γ6) exciton transition, the bowing of the energy difference between A and C exciton, and the broadening of the exciton lines clearly demonstrate the importance of disorder effects in these mixed crystals. This conclusion is further supported by the stress‐induced enhancement of the A(Γ6) exciton transition probability by uniaxial stress parallel to the c‐axis of the mixed crystals. The experimental results are discussed on the basis of an effective exciton Hamiltonian consisting of a quasi‐cubic VCA‐Hamiltonian for wurtzite‐type mixed crystals and an additional lower‐symmetric term which describes the disorder effects phenomenologically by two fluctuating crystal fields parallel and perpendicular to the c‐axis, respectively. Copyright © 1979 WILEY‐VCH Verlag GmbH & Co. KGaA