Abnormal magnetoresistance in fine-grained polycrystalline silicon layers of SOI structures

The magnetotransport properties of polycrystalline silicon layers in silicon-on-insulator (SOI) structures were studied at low temperatures down to 4.2 K and in magnetic fields up to 14 T. Experimental results reveal both negative and anomalous positive magnetoresistance in nonuniform polycrystalline silicon films, depending on the level of p-type doping near the metal–insulator transition. Low-temperature behavior of the magnetoresistance is caused to the trapping of free charge carriers at grain boundary defects. The estimated Curie temperatures for highly defective polycrystalline layers in SOI structures show both positive and negative values, indicating the coexistence of ferromagnetic and s–d antiferromagnetic interactions. In lightly doped samples with NB = 2.4⋅1018 cm–3, the negative magnetoresistance is associated with the ordering of localized spins, in samples with NB = 3.9⋅1019 cm–3, it is dominated by the polarization of conduction carriers and their additional scattering by localized magnetic moments near grain boundaries. Interaction between charge carriers within the framework of hopping conductivity in doubly occupied localized states (in the temperature range of 4.2–20 K), due to spin-dependent scattering in polycrystalline silicon films with NB = 3.9⋅1019 cm–3, can serve as a model analogy for understanding related effects in high-temperature superconductors, in particular pseudogap behavior and unconventional superconducting carrier pairing.