Multi-channel magnetotransport in Co2FeSi/(Al,Ga)As spin-LEDs

We have performed Hall effect measurements on Co₂FeSi/(Al,Ga)As spin light emitting diodes and have found unique field dependencies that differ strongly from the expected behaviors for both the ferromagnetic Co₂FeSi layer and the underlying semiconductor structure. To understand such unique field dependencies, we have developed a multi-channel transport model for parallel transport through a ferromagnet and a semiconductor. By applying this model to our data for the Hall and sheet resistance, we extract values for the carrier density and mobility in the semiconductor layer. We find that these values decrease with increasing growth temperature of the Co₂FeSi layer, presumably due to stronger in-diffusion of Co and Fe impurities, which compensate the n-type dopants in the underlying n-(Al, Ga) As layer. Despite such compensation, spin-LEDs with the Co₂FeSi layer grown at the relatively high temperature of 280 °C exhibit the highest spin injection efficiencies of more than 50%, hence calling into question the requirement of electron tunneling through the ferromagnet/semiconductor Schottky barrier for efficient spin injection.