We report electrical spin injection, transport, and detection at room temperature through band-to-band tunneling (BTBT) at semiconductor $p$-$n$ junctions. Using germanium-based lateral spin-valve devices with $p$-$n$-junction electrodes, we experimentally observe pure spin-current transport through BTBT at room temperature. Asymmetric bias-current dependence of the spin signals is evidently found, which originates from the spin injection via BTBT through $p$-$n$ junctions or the spin extraction via localized states near $p$-$n$ junctions. Notably, even for the use of a thin $p$-type semiconductor layer at the spin injector and detector, we find clear spin-transport properties at room temperature. This study will open a path for the room-temperature operation of a spin-based tunnel field-effect transistor with a $p$-$n$ junction.

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• Spin current
• Spin injection
• Transport phenomena
• Elemental semiconductors
• Field-effect transistors
• Magnetic multilayers
• Spin valves
• Tunnel junctions