Spin accumulation near Fe/GaAs (001) interfaces: The role of semiconductor band structure

We show that the degenerate region which forms in the vicinity of the Fe/GaAs (001) interface in Schottky tunnel barrier heterostructures plays an important role in spin transport. First, it is a prerequisite for a significant spin current to exist in the absence of an applied bias voltage, which is essential for electrical spin detection. Second, it establishes a well-defined electrochemical potential reservoir which functions as the source of spin currents flowing into the bulk of the semiconductor. A rate-equation analysis shows that the optimal thickness of the highly doped GaAs layer at the interface is in the range of 20 to 25 nm for Si dopings of 5×1018 cm^-3, in reasonable agreement with experiment. Both the sign and magnitude of the spin currents are sensitive to very small changes in interfacial electronic structure, as demonstrated in annealing experiments.