Large positive magnetoresistive effect in silicon induced by the space-charge effect

Abstract

Recent discoveries of large magnetoresistance in non-magnetic semiconductors^{1,2,3,4,5,6,7,8} have gained much attention because the size of the effect is comparable to, or even larger than, that of magnetoresistance in magnetic systems^{9,10,11,12,13,14}. Conventional magnetoresistance in doped semiconductors is straightforwardly explained as the effect of the Lorentz force on the carrier motion¹⁵, but the reported unusually large effects imply that the underlying mechanisms have not yet been fully explored. Here we report that a simple device, based on a lightly doped silicon substrate between two metallic contacts, shows a large positive magnetoresistance of more than 1,000 per cent at room temperature (300 K) and 10,000 per cent at 25 K, for magnetic fields between 0 and 3 T. A high electric field is applied to the device, so that conduction is space-charge limited^16,17,18. For substrates with a charge carrier density below ∼10¹³ cm^-3, the magnetoresistance exhibits a linear dependence on the magnetic field between 3 and 9 T. We propose that the observed large magnetoresistance can be explained by quasi-neutrality breaking of the space-charge effect, where insufficient charge is present to compensate the electrons injected into the device. This introduces an electric field inhomogeneity, analogous to the situation in other semiconductors in which a large, non-saturating magnetoresistance was observed^1,2,3,4,5,19. In this regime, the motions of electrons become correlated, and thus become dependent on magnetic field. Although large positive magnetoresistance at room temperature has been achieved in metal–semiconductor hybrid devices^6,7,8, we have now realized it in a simpler structure and in a way different from other known magnetoresistive effects^{9,10,11,12,13,14,20}. It could be used to develop new magnetic devices from silicon, which may further advance silicon technology.