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2009 SEMICONDUCTORS AND NANOSTRUCTURESMagnetoresistance in β-FeSi 2 on n-type Si substratesHall bars consisting of 30nm of FeSi were deposited by DCmagnetron sputtering at 30 W in a high vacuum onto nativeoxide Si (001) on to n-type phosphorous doped Si substrateswith 1-10 Ω resistivity. Post deposition the films were annealedfor 10 hours at 850 ◦ C . At these temperatures withthe breakdown of the native oxide, the film harvested theunderlying Si. X-ray diffractometry confirmed β-FeSi 2 asthe final stable phase upon the substrate. Once this wasconfirmed, Cu top electrodes were deposited, also definedusing shadow masking during sputtering. The resistance ofthe bilayer structure was measured using standard 4 wirelock-in techniques in magnetic fields, H, up to 22 T. Themagnetoresistance, MR=∆R/R, was then calculated fromthe following equation:A similarly large positive MR has been observed in borondoped Si [Schoonus et al., Phys. Rev. Lett., 100, 127202(2008)]. This effect has been attributed to autocatalytic impactionisation in the Si. They observe isotropic MR unlikethe MR in our system. All data displayed is in the transversefield (magnetic field perpendicular to the current direction),when the current and magnetic field direction concura smaller effect is measured.∆RRR(H) − R(0)= , (11)R(0)Figure 63: MR at the crossover between conduction through thefilm and substrate. Above 20 K an external magnetic field increasesthe substrate resistance until it becomes comparable to thefilm at which point the relatively smaller MR in the film is observed.At 14.4 K it is assumed that all conduction is through theβ-FeSi 2 and 11 % MR is measured.Figure 62: MR of the bilayer, the peak MR, arising from the Sioccurs at ∼45K. Below this temperature the β-FeSi 2 layer resistanceis lower than the Si and with the change in current path theMR tends to plateau.At high temperatures the resistance of the film far exceededthat of the substrate, therefore the majority of the currentshunted through the substrate. At these temperatures themagnetoresistance of the doped Si substrate is apparent.This large positive MR has recently observed in phosphorousdoped silicon [Delmo et al., Nature, 457, 1112 (2009)],explained in terms of breaking of the space charge effect.The extraordinarily large MR saturates as the substrate resistancecompares to that of the film. Figure 62 illustratesthe MR in the doped Si. This MR increases with decreasingtemperatures until the majority of the conduction is throughthe β-FeSi 2 film. At low temperatures (∼25 K) the Si substrateresistance exceeds the film and it can be assumed thatconduction is predominantly directed through the β-FeSi 2layer. This is demonstrated in figure 63, suggesting thecrossover between the two regimes. The large MR of theSi underlayer is increased by the external magnetic field.As this resistance exceeds begins to exceed that of the filmonly the MR inherent to the β-FeSi 2 layer is observed. Theexternal magnetic field creates a non linear Hall effect thatwas measured simultaneously to the MR. The non-linearityis most pronounced below 30K where the high magneticfields, and large MR of the doped Si causes the conductionpath to change.D. K. MaudeN. A. Porter, C. H. Marrows, (School of Physics and Astronomy, University of Leeds, Leeds, UK, LS2 9JT),47