Präzession optisch ausgerichteter Elektronenspins in der Schottky-Randschicht von GaAs

In photoemission of spin-polarized electrons from GaAs-surfaces with negative electron affinity (where the minimum of the $\Gamma_{6}$-conduction band in the bulk lies above the vacuum level), two new phenomena were shown to exist which are based on the lifting of the spin-degeneracy of conduction-band states in semiconductors without inversion symmetry. Connected to the spin-splitting of the conduction band there is a precessional motion of the polarization vector $\underline{P}$ of optically spin-oriented photoelectrons. This precession strongly depends on the crystal-momentum. During the transport of "hot" and "thermalized" electrons through the band-bending region near the surface the precession leads to a rotation of the polarization vector away from its initial directioncreated by the optical excitation. The precession-angle which can reach over 30$^\circ$, critically depends on the surface band-bending (in the Schottky-depletion-layer). This effect in turn was used to characterize GaAs surfaces after different surface treatments. Measurements of the spin-precession as a function of the electronkinetic energy (energy-resolved measurements) together with model calculations provide new information about the photoemission process, in particular about the change of the momentum distribution during thermalisation of "hot" photoelectrons. In experiments using optical excitation with linearly polarized light, the observation of a spin-polarization of the emitted electrons along a certain crystallographic axis gave direct evidence for the spin-splitting of the conduction band. At the same time this demonstrates a new method to extract spin-polarized electrons from single-crystal semiconductors