Exciton magnetic polarons in the semimagnetic alloys Cd1-x-yMnxMgyTe.

Abstract

The semimagnetic semiconductors ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Mn}}_{\mathit{x}}$${\mathrm{Mg}}_{\mathit{y}}$Te grown by molecular-beam epitaxy have been studied by photoluminescence and photoluminescence excitation spectroscopy. It is shown that the Zeeman splittings of exciton states depend on the Mn content only and are independent of the Mg content, i.e., the carrier--Mn spin-exchange constants are not affected by the Mg incorporation. Exciton magnetic polarons have been studied using the method of selective excitation of the exciton luminescence. The partial substitution of Cd by Mg leads to a strong increase of the magnetic polaron energy from 12 meV in ${\mathrm{Cd}}_{0.85}$${\mathrm{Mn}}_{0.15}$Te to 28 meV in ${\mathrm{Cd}}_{0.70}$${\mathrm{Mn}}_{0.14}$${\mathrm{Mg}}_{0.16}$Te. This result emphasizes the strong dependence of the polaron energy on the conditions of the primary localization of the excitons. Time-resolved photoluminescence measurements yield polaron formation times of about 100 ps without pronounced differences between the quaternary and ternary alloys. But the gain in polaron energy within a fixed time interval increases with increasing Mg content. The independently controllable variation of magnetic and nonmagnetic properties in ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Mn}}_{\mathit{x}}$${\mathrm{Mg}}_{\mathit{y}}$Te alloys allows us to demonstrate the importance of the primary localization of excitons for the magnetic polaron formation in ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Mn}}_{\mathit{x}}$${\mathrm{Mg}}_{\mathit{y}}$Te as well as in ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te alloys.