Electrical injection and detection of spin accumulation in Ge at room temperature

TL;DR

This study demonstrates room-temperature electrical spin injection and detection in germanium using Fe/MgO contacts, revealing spin lifetimes up to 123 ps and highlighting the influence of doping levels on spin transport properties.

Contribution

First demonstration of room-temperature electrical spin injection and detection in germanium with detailed spin lifetime and diffusion length measurements.

Findings

Significant spin accumulation observed at room temperature in Ge.

Spin lifetime increases from 50 ps to 123 ps as electron density decreases.

Spin resistance-area product aligns with theory below MIT but exceeds it above MIT.

Abstract

We inject spin-polarized electrons from an Fe/MgO tunnel barrier contact into n-type Ge(001) substrates with electron densities 2e16 < n < 8e17 cm-3, and electrically detect the resulting spin accumulation using three-terminal Hanle measurements. We observe significant spin accumulation in the Ge up to room temperature. We observe precessional dephasing of the spin accumulation (the Hanle effect) in an applied magnetic field for both forward and reverse bias (spin extraction and injection), and determine spin lifetimes and corresponding diffusion lengths for temperatures of 225 K to 300 K. The room temperature spin lifetime increases from {\tau}s = 50 ps to 123 ps with decreasing electron concentration, as expected from electron spin resonance work on bulk Ge. The measured spin resistance-area product is in good agreement with values predicted by theory for samples with carrier densities below the metal-insulator transition (MIT), but 100x larger for samples above the MIT. These data demonstrate that the spin accumulation measured occurs in the Ge, although dopant-derived interface or band states may enhance the measured spin voltage above the MIT. We estimate the polarization in the Ge to be on the order of 1%.