PHOTOLUMINESCENCE QUANTUM EFFICIENCY OF VARIOUS TERNARY II-VI SEMICONDUCTOR SOLID-SOLUTIONS

As a result of the spatial localization of excitons in II-VI mixed cry stals the external luminescence quantum efficiency eta(lum), is expect ed to be remarkably higher than in the corresponding binary compounds. To investigate this assumption we built a new experimental setup with a miniature integrating sphere fitted into a cryostat. At low tempera tures in the binary systems CdS and CdSe we always found eta(lum) less than or equal to 25% in the main luminescence bands (arising from bou nd excitons ((DX)-X-0, A(0)X) and donor-acceptor pair recombination). For the free-exciton luminescence eta(lum) was more than two orders of magnitude less. In contrast, CdS1-xSex mixed crystals show eta(lum) u p to 70% in the luminescence from localized states, indicating that th e nonradiative recombination is strongly suppressed for localized exci tons. Other II-VI alloys (ZnSe1-xTex, Zn1-xCdxS and Zn1-xCdxSe) show p artly considerably lower values for eta(lum). The temperature dependen ce of eta(lum), gives information about various activation processes t o nonradiative recombination channels. (C) 1998 Elsevier Science B.V. All rights reserved.