Spin injection in LEDʹs and in unipolar devices

Spin-LEDʹs have been used as a powerful tool to demonstrate the electrical injection of spin-polarized carriers into a semiconductor. We first give a review of some of the injector strategies that have been used (oxide-based tunnel injectors, highly doped Schottky tunnel injectors and magnetic semiconductors) with focus on the obtained spin polarizations and the bias dependence of these polarizations. We then move to the electrical aspects of the contacts and show that these should not be overlooked. The oxide-based tunnel injectors suffer from a large parasitic hole current when they are used in a spin-LED, and may become incapable of injecting any electrons in an all-electrical (unipolar) injection-detection device. We discuss the origin of this effect and point out possible solutions both for III–V semiconductors and for Si.