Electrical detection of spin accumulation and relaxation in p -type germanium

Abstract

We report on electrical measurements of spin-dependent transport of holes in all-epitaxial CoFe/$p$-type germanium $(p\text{\ensuremath{-}}{\mathrm{Ge})/\mathrm{Fe}}_{3}\mathrm{Si}$ spin valves, where the hole concentration $({p}_{\mathrm{h}})$ of the $p$-Ge layer is estimated to be $\ensuremath{\sim}{10}^{18}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. Spin-accumulation output voltages can electrically be detected in the antiparallel magnetization state between CoFe and ${\mathrm{Fe}}_{3}\mathrm{Si}$ ferromagnetic electrodes. The room-temperature spin lifetime of holes in the $p$-Ge layers can tentatively be discussed in terms of the theory by Fert and Jaffr\`es. We propose that the use of (111)-oriented $p$-Ge with a hole concentration of $\ensuremath{\sim}{10}^{18}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ enables the transport of spin-polarized holes in bulk Ge even at room temperature.