  The spin field effect transistor envisioned by Datta and Das opens a gateway
to spin information processing. Although the coherent manipulation of electron
spins in semiconductors is now possible, the realization of a functional spin
field effect transistor for information processing has yet to be achieved,
owing to several fundamental challenges such as the low spin-injection
efficiency due to resistance mismatch, spin relaxation, and the spread of spin
precession angles. Alternative spin transistor designs have therefore been
proposed, but these differ from the field effect transistor concept and require
the use of optical or magnetic elements, which pose difficulties for the
incorporation into integrated circuits. Here, we present an all-electric and
all-semiconductor spin field effect transistor, in which these obstacles are
overcome by employing two quantum point contacts as spin injectors and
detectors. Distinct engineering architectures of spin-orbit coupling are
exploited for the quantum point contacts and the central semiconductor channel
to achieve complete control of the electron spins -- spin injection,
manipulation, and detection -- in a purely electrical manner. Such a device is
compatible with large-scale integration and hold promise for future spintronic
devices for information processing.
