Spin coherence in semiconductors: storage, transport and reduced dimensionality

We review the use of femtosecond-resolved optical techniques for the study of electron spin dynamics in semiconductors and show how these methods are able to address many of the issues that are centrally important to spin pol arized semiconductor-based electronics. pump-probe studies can be used to o ptimize spintronic material parameters, and have led to the observation of 100 ns spin lifetimes in n-doped bulk GaAs and spin transport across macros copic length scales (100 mum). We have found that spin coherence is preserv ed across a semiconductor heterojunction over a broad range of temperatures , and can be protected by transport to regions of intrinsically lower decoh erence. Studies of CdSe quantum dots ranging from 22 To 80 Angstrom in diam eter indicate that spin coherence in these structures is thermally robust. with nanosecond-scale spin lifetimes persisting to room temperature. (C) 20 01 Elsevier Science B.V. All rights reserved.