Spin injection from the Heusler alloy Co/sub 2/MnGe into Al/sub 0.1/Ga/sub 0.9/As/GaAs heterostructures

Abstract

Co/sub 2/MnGe epitaxial films were grown by molecular beam epitaxy (MBE) on Al/sub 0.1/Ga/sub 0.9/As [001] surfaces prepared in a separate MBE-growth chamber and transferred in ultra high vacuum (<10/sup -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 Co/sub 2/MnGe films have saturation magnetization of 1000 emu/cm/sup 3/ 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 Co/sub 2/MnGe formed Schottky contact on n-Al/sub 0.1/Ga/sub 0.9/As 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/Co/sub 2/MnGe/n+/n- Al/sub 0.1/Ga/sub 0.9/As/ i - Al/sub 0.1/Ga/sub 0.9/As / i-GaAs (100 /spl Aring/) / i-Al/sub 0.1/Ga/sub 0.9/As/p-Al/sub 0.1/Ga/sub 0.9/As heterostructures. The 70 /spl Aring/ thick Co/sub 2/MnGe Schottky barrier injector was grown at 175/spl deg/C and the 25 /spl Aring/ thick Al capping layer used to prevent oxidation during exposure to air was grown at 0/spl deg/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.