Electron Charge and Spin Transport in Ferromagnet/Semiconductor Schottky Barrier Heterostructures

Previous studies of Fe/$n^+$-GaAs/$n$-GaAs heterostructures in the lateral non-local geometry have shown that spin accumulation is observed only when tunneling current across ferromagnet/semiconductor Schottky barrier is sufficiently large. The tunneling mechanism is modeled by band diagram simulations and transport calculation using the WKB approximation for the barrier. These suggest that tunneling from localized states in the quantum well (QW) which forms just inside the Schottky interface dominates over tunneling directly from the semiconductor bulk. Electron tunneling spectroscopy is utilized to probe the predicted localized states in the QW. Valleys in the derivative of tunneling conductance spectra were observed at discrete forward bias voltages which are attributed to localized 2-dimensional energy states. The spin escape time of the 2D energy states in the QW is calculated using a spin-dependent WKB approximation. The results are compared with the spin lifetime and escape time extracted from three-terminal spin Hanle measurements. This work was supported by the NSF MRSEC and ONR MURI programs, and NSF DMR-0804244.