Characterization of embedded MgO/ferromagnet contacts for spin injection in silicon

Abstract

In this work we present the structural and electrical characterization of sputter-deposited CoFe(B)/MgO/Si metal-insulator-semiconductor tunneling junctions for injection and detection of spin polarized current in silicon. The multilayers have been deposited in 700 nm deep trenches, patterned in thick SiO2 dielectric, on n- and p-doped wafers. The films inside the trenches are continuous with a correlated and low roughness. The MgO barrier grows amorphous without indication of pinholes. The dc and ac transport properties of the junctions were studied as a function of temperature and frequency. A relatively high interface trap density at the MgO/Si-interface is extracted from admittance spectra measurements. Transport is dominated by majority carriers in the case of n- doped and by minority carriers for the p-doped wafers. This leads to distinct rectification characteristics for the two wafer types, which would significantly influence the spin injection efficiency of the tunneling junctions

Spin injection from Fe into Si(001):Ab initiocalculations and role of the Si complex band structure

“…Efficient spin injection has been found in FeCo/MgO/GaAs and FePt/MgO/GaAs junctions, 7 while work in this direction has been reported also for FeCoB/ MgO/Si junctions. 15 A reduction of efficiency can also be caused by the formation of iron silicide at the interface, which can sometimes lead to noncollinear magnetic ordering. This can be avoided by inserting a nonmagnetic metal between Fe and Si ͑as was done, e.g., in Refs.…”

“…7 Most works have focused on injection into GaAs, [5][6][7][8] where the current polarization can be detected optically in GaAs/ AlGaAs/GaAs quantum wells or electrically in lateralgeometry experiments. 8 Recently, however, electrical spin injection into Si has also been demonstrated via electrical spin detection, [9][10][11][12] nonlocal electrical detection, 12 and optical detection, 13 with impressively large spin coherence length, reaching up to 350 m. 11 The present work was motivated by the increasing experimental activity in the direction of spin injection and manipulation in Si, [9][10][11][12][13][14][15] as well as by arguments for advantages of spin transport in Si. 16 Based on density-functional calculations we examine the possibility of direct spin injection from Fe into Si, with the Schottky barrier of Si used as the necessary tunneling barrier.…”

Introduction to spin-polarized ballistic hot electron injection and detection in silicon

“…Subsequently, several efforts to tune the FMSi interface resistance were made [47][48][49][50][51]. However, despite the ability to tune the RA product by over eight orders of magnitude and even into the anticipated high-magnetoresistance window (for instance, by using a low-work-function Gd layer), no evidence that this approach has been fruitful for Si can be found, and the theory has yet been confirmed only for the case of low-temperature-grown 5 nm thick GaAs [52,53].…”

Electron energy band alignment at the (100)Si/MgO interface

“…6,7 In particular, MgO is widely used as a barrier in magnetic tunnel junctions ͑MTJs͒ [8][9][10] with the recently demonstrated possibility of spin injection into the silicon crystal. 11,12 In all these applications, MgO is supposed to serve as an insulator providing high energy barriers for electrons and holes. Though the knowledge of the barriers is of particular importance for MTJs as they determine the type of charge carriers that provide the dominant contribution to the tunneling current, 11 the band alignment between MgO and silicon, the most relevant for device fabrication, has not been addressed yet experimentally.…”

“…11,12 In all these applications, MgO is supposed to serve as an insulator providing high energy barriers for electrons and holes. Though the knowledge of the barriers is of particular importance for MTJs as they determine the type of charge carriers that provide the dominant contribution to the tunneling current, 11 the band alignment between MgO and silicon, the most relevant for device fabrication, has not been addressed yet experimentally. One of the reasons for this lack of information concerns the strong impact of the x-ray induced insulator charging 13 which in the case of MgO has been quoted as "commonly catastrophic."…”