Abstract
cw and time-resolved photoluminescence spectroscopy is used to study ZnSe/Se quantum wells with semimagnetic barriers in an external magnetic field. The data demonstrate a change of the dominant energy relaxation mechanism from disorder localization of light-hole excitons at zero-field to heavy-hole exciton interface magnetic polaron formation at intermediate fields and, again, disorder localization of heavy-hole excitons at large magnetic fields. The formation of the interface magnetic polaron is promoted by a magnetic-field-induced type-I–type-II transition for heavy-hole excitons. Despite the transition, neither the exciton lifetime nor its optical oscillator strength is dramatically altered. This is, as we confirm by numerical solution of the two-particle Schrödinger equation, a result of the electron-hole Coulomb interaction. The polaron formation time is initially 110 ps, but decreases with growing magnetic field down to 70 ps (B=5 T). A theoretical investigation of the polaron formation dynamics shows that the associated change of the exciton wave function is smaller, the closer the spin system is driven into saturation by the external field. As a consequence, the polaron formation time approaches the characteristic spin response time. Our measurement uncovers a fast primary localization prior to the polaron process—but also of magnetic origin—that we believe to be necessary to start the polaron formation. © 1996 The American Physical Society.
- Received 22 December 1995
DOI:https://doi.org/10.1103/PhysRevB.53.16444
©1996 American Physical Society