Magneto-optical spectroscopy of spin injection and spin relaxation in ZnMnSe/ZnCdSe and GaMnN/InGaN spin light-emitting structures

In this paper we review our recent results from in-depth investigations of physical mechanisms which govern efficiency of several processes important for future spintronic devises, such as spin alignment within diluted magnetic semiconductors (DMS), spin injection from DMS to non-magnetic spin detectors (SDs) and also spin depolarization within SD. Spin-injection structures based on II-VIs (e.g. ZnMnSe/Zn(Cd)Se) and III-Vs (e.g. GaMnN/Ga(In)N) were studied as model cases. Exciton spin relaxation within ZnMnSe DMS, important for spin alignment, was found to critically depend on Zeeman splitting of the exciton states and is largely facilitated by involvement of longitudinal optical (LO) phonons. Optical spin injection in ZnMnSe/Zn(Cd)Se was shown to be governed by (i) commonly believed tunneling of individual carriers or excitons and (ii) energy transfer via localized excitons and spatially separated localized electron-hole pairs (LEHP) located within DMS. Unexpectedly, the latter mechanism is in fact found to dominate spin injections. We shall also show that spin depolarization in the studied structures is essentially determined by efficient spin relaxation within non-magnetic spin detectors, which is an important factor limiting efficiency of spin detection. Detailed physical mechanisms leading to efficient spin depolarization will be discussed.