Spin polarized transports through a narrow-gap semiconductor wire with ferromagnetic contacts formed on InAlAs step-graded buffer layers

We investigated the transport properties of ferromagnetic/semiconductor hybrid structures utilizing an InAs/In_0.75Al_0.25As modulation-doped heterostructures formed on a GaAs (001) substrate with In_xAl_1−xAs step-graded buffer layers. We used NiFe as ferromagnetic electrodes for injection/detection of spin-polarized electrons, which were formed on side walls of the semiconductor mesa to contact electron channel directly. We measured magneto-transport properties of the samples with current flow between the ferromagnetic electrodes at low temperatures. Under vertical magnetic fields, magneto-resistance oscillations were clearly observed, thus the ferromagnetic electrodes worked as ohmic contacts. In addition, we successfully found spin-valve properties under parallel magnetic fields. Furthermore, we observed the enhancement of spin-valve properties by squeezing the channel width.