Extremely large magnetoresistance induced by optical irradiation in the Fe/SiO_2/p-Si hybrid structure with Schottky barrier

摘要

We report giant magnetoresistance (MR) effect that appears under the influence of optical radiation in common planar device built on Fe/SiO_2/p-Si hybrid structure. Our device is made of two Schottky diodes connected to each other by the silicon substrate. Photo-induced MR is positive and the MR ratio reaches the values in excess of 10~4%. The main peculiarity of the MR behavior is its strong dependence on the magnitude and the sign of the bias current across the device and, most surprisingly, upon polarity of the magnetic field. To explain such unexpected behavior of the MR, one needs to take into account contribution of several physical mechanisms. The main contribution comes from the existence of localized interface states at the SiO_2/p-Si interface, which provide the spots for the photo-current conduction by virtue of the sequential tunneling through them or thermal generation and optical excitation of mobile charges. External magnetic field changes the probability of these processes due to its effect on the energy states of the conduction centers. Two possible mechanisms that may be responsible for the observed dependence of magneto-resistance on the field polarity are discussed: the effect of the Lorentz force on moving carriers and spin splitting of electrons moving in the electrostatic potential gradient (Rashba effect). The most significant observation, in our opinion, is that the observed MR effect is seen exclusively in the subsystem of minority carriers transferred into non-equilibrium state by optical excitation. We suggest that building such magneto-sensitive devices based on this mechanism may set a stage for new types of spintronic devices to emerge.