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Spectrally resolved optical study of transient spin dynamics in semiconductors

TitleSpectrally resolved optical study of transient spin dynamics in semiconductors
Publication TypeThesis
Year of Publication2006
AuthorsChen, Z

Using the spin of the electron to carry information, instead of or in addi- tion to its charge, could provide advances in the capabilities of microelectronics. Successful implementation of spin-based electronics requires preservation of the electron spin coherence. Long spin coherence times have been observed in lightly n-doped semiconductors, with a maximum at a “magic” electron density. We sys- tematically study the spin dynamics of the electron in a GaAs quantum well, where the electron density in the well can be varied through optical excitation. We show that spin coherence is lost due to the interplay between localization by disorder and dynamical scattering. The disorder potential is characterized by measuring the electron Landé g factor dependence on density. Our results show that the longest spin coherence is obtained for weakly localized spins, which may dictate a compromise in the design of devices between increasing the spin coherence time and improving transport properties.
We also explore the intimate connection between electron spin and optical excitation that initiates and controls the spin states. We study the interplay of spin dynamics between excitons, negatively charged excitons and the two-dimensional electron gas in a lightly n-doped semiconductor quantum well. The spin of the electron gas can be polarized through interband transitions, and the electron spin can persist long after the recombination of optically excited carriers. We find that the excitation of spin polarization of the resident electrons depends on the recombination times and spin relaxation times of the optically excited carriers and the energy chosen for the light pulses.