Electrical Spin Injection into Silicon Nanowires with Axial Doping Gradient*

For nanoscopic semiconductor spintronic devices, the all-important issue of the ferromagnet/semiconductor (FM/SC) interface becomes even more critical. Here we elucidate the effects of the FM/SC nano interface on electrical spin injection and detection, utilizing a unique type of Si nanowires (NWs) with an inherent axial doping gradient. Two-terminal and nonlocal four-terminal lateral spin-valve measurements were performed using different combinations from a series of FM contacts positioned along the same NW. The data are analyzed with a general model of spin accumulation in a normal channel under electrical spin injection from a FM, which reveals a distinct correlation of decreasing spin-valve signal with increasing injector junction resistance.¹ The observation is attributed to the diminishing contribution of the d-electrons in the FM to the injected current spin polarization with increasing Schottky barrier width. The results demonstrate that there is a window of interface parameters for optimal spin injection efficiency and current spin polarization, which provides important design guidelines for nano-spintronic devices with quasi-1D semiconductor channels.
¹K. Kountouriotis et al., Nano Lett. 18, 4386 (2018)