Spin injection from the Heusler alloy Co2MnGe into Al0.1Ga0.9As/GaAs heterostructures

Co₂MnGe epitaxial films were grown by molecular beam epitaxy (MBE) on Al_0.1Ga_0.9As [001] surfaces prepared in a separate MBE-growth chamber and transferred in ultra high vacuum (<10^-10 torr) to the Heusler alloy MBE growth chamber. In-situ RHEED, ex-situ XRD and TEM demonstrate single crystal epitaxial growth of the films. In-plane VSM measurements showed that the Co₂MnGe films have saturation magnetization of 1000 emu/cm³ at room temperature and a coercivity of 8 Oe. A SQUID magnetometer was used to measure the out of plane magnetization, which was found to saturate around 0.8 Tesla. We found that Co₂MnGe formed Schottky contact on n-Al_0.1Ga_0.9As with 0.82 eV barrier height with ideality factor of 1.03. In order to measure the spin injection, tunneling Schottky barrier contact spin-LED structures were fabricated from MBE-grown Al/Co₂MnGe/n+/n- Al_0.1Ga_0.9As/ i - Al_0.1Ga_0.9As / i-GaAs (100 Å) / i-Al_0.1Ga_0.9As/p-Al_0.1Ga_0.9As heterostructures. The 70 Å thick Co₂MnGe Schottky barrier injector was grown at 175°C and the 25 Å thick Al capping layer used to prevent oxidation during exposure to air was grown at 0°C. The epitaxial heterostructures were processed into LED devices and the devices were operated with the Schottky contact under reverse bias and the p-i-n LED under forward bias. Electroluminescence was collected along the sample normal. The circular polarization of the observed electroluminescence was 14% indicating a spin injection of 14% at 2 K. The injected spin polarization at 2 K was calculated to be 27% based on a calibration of the spin detector using Hanle effect measurements.