Spin injection and spin dynamics at the CuPc/GaAs interface studied with ultraviolet photoemission spectroscopy and two-photon photoemission spectroscopy

Abstract

Interface formation between $p$-type GaAs(100) and the organic semiconductor copper phthalocyanine (CuPc) has been studied with ultraviolet photoemission spectroscopy and two-photon photoemission spectroscopy (2PPE). Spin-resolved 2PPE measurements show a highly efficient spin injection of hot electrons from GaAs into CuPc, demonstrating that spin-polarized electrons originating from the GaAs substrate can be injected into CuPc without any substantial spin-flip scattering at the interface. Furthermore, spin- and time-resolved 2PPE measurements are employed to study the temporal evolution of the spin polarization injected into the organic layer in the range up to 1 ps after injection from the GaAs substrate. The results show that the degree of spin polarization of electrons injected through the GaAs/CuPc interface into molecular orbitals just above the lowest unoccupied molecular orbital onset of CuPc is preserved longer than the spin polarization of electrons injected in energetically higher lying states.