Ultrafast low-power spin-injection devices based on modified ferromagnetic-semiconductor junctions

The authors describe recent theoretical and experimental advances in achieving large accumulated spin polarisation in semiconductors and suggest new classes of low-power ultrafast devices. Tunnelling of electrons between nonmagnetic semiconductors (S) and ferromagnets (FM) through a Schottky barrier modified by a δ-doped layer at the interface is described. It is shown that, in such reverse (forward) biased FM-S junctions, electrons with a certain spin projection can be efficiently injected in (extracted from) S, while electrons with the opposite spin can efficiently accumulate in S near the interface. This occurs due to spin filtering of electrons in the tunnelling process, and the authors found conditions for most efficient accumulation of spin polarisation. Extraction of spin can proceed in degenerate semiconductors at low temperatures. Novel spin-valve ultrafast devices with small dissipated power are described: a magnetic sensor, a spin transistor, an amplifier, a frequency multiplier, a square-law detector and a source of polarised radiation.