Increase in spin injection efficiency of a CoFe∕MgO(100) tunnel spin injector with thermal annealing

Postgrowth thermal annealing of a CoFe∕MgO(100) tunnel spin injector grown on aGaAs∕AlGaAs quantum well structure results in a significantly increased spin injection efficiency as inferred from the polarization of heavy-hole electroluminescence from a quantum well optical detector. The as-deposited sample displayed an initial polarization at 100K of 43%, which was increased to 52% after a 1h anneal at 300°C, and finally to 55% after a second 1h anneal at 340°C. The polarization remained unchanged upon further annealing to temperatures as high as 400°C. These results show that tunnel spin injectors based on CoFe∕MgO are robust with high thermal stability, making them useful for device applications.