Observation of intravalley spin scattering in a doped multivalley semiconductor

To clarify spin-related phenomena within a single conduction valley of multivalley semiconductors, we experimentally study the effect of carrier concentration $(n)$ on spin lifetime $({\ensuremath{\tau}}_{\mathrm{S}})$ in strained ${\mathrm{Si}}_{0.1}{\mathrm{Ge}}_{0.9}$ at various temperatures. The spin diffusion length $(\ensuremath{\lambda})$ of strained ${\mathrm{Si}}_{0.1}{\mathrm{Ge}}_{0.9}$ is estimated from the contact distance dependence of the nonlocal spin signals for spin transport measurements in lateral spin-valve devices with varying $n$. The obtained $\ensuremath{\lambda}$ is found to depend on $n$ at temperatures below $\ensuremath{\sim}100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, with the estimated ${\ensuremath{\tau}}_{\mathrm{S}}$ value at 8 K varying significantly with $n$, ranging from 0.2 to 6.2 ns. These features suggest the presence of intravalley spin scattering at low temperatures even in doped multivalley semiconductors. Thus, strained $n\text{\ensuremath{-}}{\mathrm{Si}}_{0.1}{\mathrm{Ge}}_{0.9}$ with $L$-valley energy splitting serves as a powerful tool for investigating the spin relaxation mechanisms in a single conduction valley of doped multivalley semiconductors.