Hybrid Quantum Structures

We study spin-polarized transport in quantum-systems consisting of semiconducting and ferromagnetic materials. We aim at the realization of a spin-polarized field-effect transistor (SpinFET) which has been proposed by S. Datta and B. Das in 1990 [Appl. Phys. Lett. 56, 665 (1990)]. This new type of device is based on the electron spin. The spins are injected from a ferromagnetic source electrode, the magnetization of which defines the orientation of the spins, and detected by a ferromagnetic drain electrode. In a metal-oxide-semiconductor (MOSFET) structure with ferromagnetic source and drain contacts as spin injector and analyzer, respectively, the transmission of the device can be controlled by the spin-valve effect: when the orientation of the injected spin in the semiconductor is the same as that of the analyzer the electron can transmit into the drain contact. Otherwise it will be reflected. In conventional full-metal spin-valves, the conductance is controlled by an external magnetic field which switches the spin configuration of the contacts. However, in our case instead of a normal metal a quasi two-dimensional electron system (2DES) in a narrow-gap semiconductor with strong spin-orbit interaction is employed. To be precise, the so-called Rashba-effect leads to a precession of the electron spin in the 2DES which can be tuned by a gate voltage via field-effect. By this mechanism the current between the two ferromagnetic electrodes can be changed even without applying an external magnetic field.
For this, many topics must be investigated including the micromagnetic behavior of the ferromagnetic electrodes, the spin-orbit interaction in the semiconductor, the materials as well as device geometries. Click here to see a selection of our publications.