Volume 91, Issue 10, 15 May 2002
Index of content:
- SPIN INJECTION IN FERROMAGNETIC/SEMICONDUCTOR MATERIALS
Spin injection across a hybrid heterojunction: Theoretical understanding and experimental approach (invited)91(2002); http://dx.doi.org/10.1063/1.1447282View Description Hide Description
Spin injection across a hybrid ferromagnet/semiconductor junction has proven to be difficult, unlike in an all-metal junction used in giant magnetoresistancedevices. The difference responsible is highlighted in a simple model. We perform spin-injection-detection experiments on devices with two ferromagnetic contacts on a two-dimensional electron gas confined in an InAsquantum well. We demonstrate that spin injection allows the hybrid device to combine both the advantage of the ferromagnet as well as that of the semiconductor.
91(2002); http://dx.doi.org/10.1063/1.1446125View Description Hide Description
In this article we summarize our recent work on room-temperature spin injection in Fe/GaAs and MnAs/GaAs heterostructures. The most critical issue for injection of spin polarized electrons (holes) from the ferromagnet (FM) into the semiconductor (SC) is the control of the atomic arrangement at the FM/SC interface during molecular beam epitaxial growth of these rather dissimilar materials. For many years the formation of a magnetically dead layer at the Fe/GaAs interface has prevented spin injection. In addition to the accurate control of the FM/SC interface, the formation of a Schottky barrier between FM and SC for efficient spin injection via tunneling is the second critical issue for successful experiments. We describe in detail our approaches to solve these problems.
91(2002); http://dx.doi.org/10.1063/1.1455606View Description Hide Description
Optical pumping is used to generatespin-polarized carriers in epitaxial ferromagnet-GaAs Schottky diodes with quantum wells placed in the depletion region. A strong dependence of the photocurrent on the polarization state of the incident light is observed, and a series of measurements as a function of excitation energy, bias voltage, magnetic field, and excitation geometry are used to distinguish spin-dependent transport from a variety of background effects. The spin polarization of the photocurrent for pumping energies at and above the band gap of GaAs is of order 0.5% or less. Much larger polarization dependence is observed for excitation energies near the quantum well ground state. Although background effects are very large in this regime, the field dependence of the polarization signal for several samples is suggestive of spin-dependent transport.