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△ [16a-501-6] Observation of spin transport in n-type non-degenerate germanium using Co2Fe0.4Mn0.6Si Heusler alloy electrodes
Keywords:Heusler alloy, Spin injection, Spin transport
Spin transports between two ferromagnetic (FM) electrodes on a semiconductor (SC) channel have been demonstrated by many groups using non-local Hanle and spin-valve measurements. However, the observed spin signals were small because tunneling spin polarizations P across the FM/SC junctions are considerably small. In order to enhance the spin signal, Co-based Heusler alloys are promising materials as the FM electrode because of its high spin polarization [1-2]. In addition, from an application point of view, a non-degenerate Ge is an attractive material as a channel layer [3]. In this work, we investigated spin transport in the n-type non-degenerate Ge (001) using both Co2Fe0.4Mn0.6Si (CFMS) electrodes and δ-doping technique.
We fabricated following stacked structure: Si(001) sub./undoped Ge (1000 nm)/n-Ge channel (100 nm, ~1×1018 cm-3)/Sb δ-doping layer (Sheet doping density, 2.0×1014 cm-2)/Ge re-growth layer (10 nm)/Mg (0.8 nm)/MgO (0.75 nm)/CFMS (30 nm)/Ta (5 nm). The films were respectively prepared by molecular beam epitaxy for the re-growth Ge layer and DC/RF magnetron sputtering for the MgO and CFMS layers. The devices were prepared by optical photolithography methods and Ar-ion milling.
Highly B2 ordered CFMS films were successfully obtained on the Ge/MgO layer by optimization of fabrication conditions. We measured local 3-terminal magnetoresistance (L-3T MR) and Hanle effect [4] by using the device as shown in Figure 1. Figure 2 shows typical results of the L-3T MR measurements at 10 K. The electrode 3 was placed under the spin extraction condition. A steep voltage changes (~80 µV) was successfully observed around ±20 and ±50 Oe, which corresponded to coercive fields of two CFMS electrodes measured by Kerr effect. By fitting a Hanle signal by Lorentzian curves, long spin life time (12.2 ns) and spin diffusion length (66.6 µm) were respectively evaluated. These results indicate that a spin-polarized current flows between two CFMS electrodes through the Ge channel. We have first observed the L-3T MR signal in the n-type non-degenerate Ge (001) by combination of highly ordered Co-based Heusler alloy film and δ-doping technique.
This work was supported by ImPACT Program (Program manager: Masashi Sahashi), grants-in-aid for scientific research S (No.24226001), and Interdepartmental Doctoral Degree Program for Multi-dimensional Materials Science Leaders.
We fabricated following stacked structure: Si(001) sub./undoped Ge (1000 nm)/n-Ge channel (100 nm, ~1×1018 cm-3)/Sb δ-doping layer (Sheet doping density, 2.0×1014 cm-2)/Ge re-growth layer (10 nm)/Mg (0.8 nm)/MgO (0.75 nm)/CFMS (30 nm)/Ta (5 nm). The films were respectively prepared by molecular beam epitaxy for the re-growth Ge layer and DC/RF magnetron sputtering for the MgO and CFMS layers. The devices were prepared by optical photolithography methods and Ar-ion milling.
Highly B2 ordered CFMS films were successfully obtained on the Ge/MgO layer by optimization of fabrication conditions. We measured local 3-terminal magnetoresistance (L-3T MR) and Hanle effect [4] by using the device as shown in Figure 1. Figure 2 shows typical results of the L-3T MR measurements at 10 K. The electrode 3 was placed under the spin extraction condition. A steep voltage changes (~80 µV) was successfully observed around ±20 and ±50 Oe, which corresponded to coercive fields of two CFMS electrodes measured by Kerr effect. By fitting a Hanle signal by Lorentzian curves, long spin life time (12.2 ns) and spin diffusion length (66.6 µm) were respectively evaluated. These results indicate that a spin-polarized current flows between two CFMS electrodes through the Ge channel. We have first observed the L-3T MR signal in the n-type non-degenerate Ge (001) by combination of highly ordered Co-based Heusler alloy film and δ-doping technique.
This work was supported by ImPACT Program (Program manager: Masashi Sahashi), grants-in-aid for scientific research S (No.24226001), and Interdepartmental Doctoral Degree Program for Multi-dimensional Materials Science Leaders.