Kohei Hamaya

Because spin‐orbit coupling in wurtzite semiconductors is relatively weak compared with that in zincblende ones, the III‐nitride semiconductor GaN is a promising material for high‐performance optical semiconductor spintronic devices such as spin lasers. For the purpose of reducing the operating power of spin lasers, it is necessary to demonstrate highly efficient electrical spin injection from a ferromagnetic material into GaN with a low‐resistance contact. Here, an epitaxial half‐metallic Heusler alloy Co 2 FeAl x Si 1− x (CFAS)/GaN heterostructure is developed by inserting an ultrathin Co layer between the CFAS and GaN. The CFAS/ n + ‐GaN heterojunctions clearly show tunnel conduction with very small rectification and a low resistance‐area product of ≈3.8 kΩµm 2 , which is several orders of magnitude smaller than those reported in previous work, at room temperature. Nonlocal spin signals and a Hanle effect curve are observed at low temperatures using lateral spin‐valve devices with the CFAS/ n + ‐GaN contacts, suggesting pure spin current transport in bulk GaN. The spin transport is observed at temperatures as high as room temperature, with a high spin polarization of 0.2 at a low bias voltage less than 2.0 V. This study is expected to open a path to GaN‐based spintronic devices with highly spin‐polarized and low‐resistance contacts.