Spin polarization in an organic semiconductor system: The spin-dependent conductivity effects

In organic semiconductor spintronic devices, the up-spin and down-spin polarons have different density once spin injection happens from ferromagnetic electrodes into organic semiconductors. For the different spin density of two spin channels could induce different conductivity, the different conductivity between the up-spin and down-spin polarons directly dominates the spin polarization. Here the effect of spin-dependent conductivity on the spin polarization is extensively studied applying the spin drift-diffusion equation on the ferromagnetic (FM)/organic (OSE) structure. It is found that the spin dependence of the electrical conductivity is induced by the spin injection and closely related to the induced spin density (or spin accumulation) μ↓-μ↑μ↓-μ↑. The calculations show that the electrical conductivity induced by up-spin polarons (down-spin polarons) is position-dependent in the OSE just as the spin accumulation. And the match level of conductivities σ0/σfσ0/σf can affect the spin-dependent conductivity at the interface of the FM/OSE to a great extent. In addition, it is found that the electric-field can affect the current spin polarization α(x)α(x) in the FM/OSE system in the low-voltage regime (eV << kBT).