Efficient spin injection and extraction in modified reverse and forward biased ferromagnetic–semiconductor junctions and low-power ultrafast spin injection devices

Abstract

This paper addresses recent theoretical and experimental advances in obtaining large spin polarization in semiconductors. In particular, we describe tunneling of electrons between nonmagnetic semiconductors (S) and ferromagnets (FM) through a Schottky barrier modified by very thin heavily doped interfacial layer. 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. This occurs due to spin filtering of electrons in a tunneling process. We find conditions for most efficient extraction and accumulation of spin and show that spin polarization of electrons near the interface can, at least in principle, be made close to 100% in nondegenerate S at room temperature and certain bias voltages. Extraction of spin can proceed in degenerate semiconductors at any (low) temperature. A new class of spin valve ultrafast devices with small dissipated power is described: a magnetic sensor, a spin transistor, an amplifier, a frequency multiplier, and a square-law detector.