Abstract
We have investigated growth characteristics and tunneling magnetoresistance (TMR) of MnAs/AlAs/MnAs trilayer heterostructures grown by molecular beam epitaxy on vicinal GaAs(1 1 1)B substrates. Since MnAs layers grown at 250°C on vicinal GaAs(1 1 1)B substrates misoriented 2° toward the [ 1 ̄ 1 ̄ 2] direction exhibited step-bunched but extremely smooth surface morphology, MnAs/AlAs/MnAs trilayers grown on this bottom layer had also very smooth interface morphology. Surface segregation of Mn atoms was found to occur during the growth of the AlAs barrier layer when the substrate temperature was 250°C or higher, resulting in the incorporation of Mn impurities in the AlAs layer. Mn impurities in the AlAs layer led to ferromagnetic interlayer coupling between the top and bottom MnAs layers and they were fatal to TMR effect. By lowering the growth temperature for the AlAs layer and for the successive top MnAs layer to 200°C, the surface segregation of Mn atoms was significantly suppressed. Then, the MnAs/AlAs/MnAs trilayers exhibited no ferromagnetic interlayer coupling, and TMR was clearly observed for the first time in this material system.
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