  Spin accumulation voltages in a non-degenerate Si spin valve are discussed
quantitatively as a function of electric bias current using systematic
experiments and model calculations. As an open question in semiconductor
spintronics, the origin of the deviation of spin accumulation voltages measured
experimentally in a non-degenerate Si spin valve is clarified from that
obtained by model calculation using the spin drift diffusion equation including
the effect of the spin-dependent interfacial resistance of tunneling barriers.
Unlike the case of metallic spin valves, the bias dependence of the
resistance-area product for a ferromagnet/MgO/Si interface, resulting in the
reappearance of the conductance mismatch, plays a central role to induce the
deviation.
