Abstract:
Spin coherence and coherent spin transport are among the central issues of semiconductor spintronics. A host of optical studies have revealed a pronounced, nonmonotonic variation of the carrier spin lifetime with the doping level in GaAs, with a peak near the insulator-metal transition (IMT). While some aspects of these intriguing observations can be understood qualitatively based on the competition between the main spin relaxation mechanisms, a full account of the nontrivial dependence of the spin lifetime with carrier density in semiconductors remains elusive. Using the persistent photoconductor Al0.3Ga0.7As as the medium, Fe/GaAs graded Schottky junctions as the spin injector, and all-electric nonlocal detection of spin accumulation/transport, we carry out a detailed examination of the carrier spin transport/relaxation as a function of its carrier concentration, especially near the IMT. Persistent photoconductivity permits in situ photodoping of the AlGaAs channel and detailed determination of the spin lifetimes in the neighborhood of the IMT, all in one and the same sample. Characterization of the photo-induced IMT in the AlGaAs epilayer and electronic properties of the Fe/AlGaAs heterostructures, as well as initial measurements of the spin accumulation/transport with varying carrier density, will be presented.