The T 1 spin lifetime of a lightly doped n-type GaAs sample has been measured via time-resolved polarization spectroscopy under a number of temperature and magnetic field conditions. Lifetimes up to 19 s have been measured. The magnetic field dependence of T 1 shows a nonmonotonic behavior, where the spin lifetime first increases, then decreases, then increases again with field. The initial increase in T 1 is understood to be due to correlation between electrons localized on donors. The decrease in T 1 is likely due to phonon-related spin-orbit relaxation. The final increase in T 1 with B indicates a suppression of the spin-orbit relaxation that may involve a level-crossing related cusp in the Rashba or Dresselhaus contributions to relaxation, or may arise from an unknown source.

We report observations of three distinct conduction mechanisms in n-type doped mixed-phase amorphous/nanocrystalline silicon thin films over a range of nanocrystallite concentrations and temperatures. As the temperature is varied from 470 to 10 K, we observe activated conduction, multiphonon hopping (MPH), and Mott variable range hopping (VRH) as the nanocrystal content is increased. The transition from MPH to Mott-VRH hopping around 50 K is tentatively ascribed to the freeze out of the phonon modes.

A detailed description of the microscopic nature of electronic conduction in mixed-phase silicon thin films near the amorphous/nanocrystalline transition is presented. A conduction model utilizing both the conductivity and the reduced activation energy data, involving the parallel contributions of three distinct conduction mechanisms, is shown to describe the data to a high accuracy, providing a clear link between measurement and theory in these complex materials.

Studies of the electronic transport properties of n-type doped hydrogenated amorphous/nanocrystalline silicon (a/nc-Si:H) films deposited in a dual-plasma co-deposition reactor are described. For these doped a/nc-Si:H, the conductivity increases monotonically for increasing crystal fractions up to 60% and displays marked deviations from a simple thermally activated temperature dependence. Analysis of the temperature dependence of the activation energy for these films finds that the dark conductivity is best described by a power-law temperature dependence, σ = σ o (T/T o ) n where n = 1 -4, suggesting multiphonon hopping as the main transport mechanism. These results suggest that electronic transport in mixed-phase films occurs through the a-Si:H matrix at lower nanocrystal concentrations and shifts to hopping conduction between clusters of nanocrystals at higher nanocrystal densities.

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