The International Technology Roadmap for semiconductors has identified the electron's spin angular momentum as a new state variable that should be explored as an alternative to the electron's charge for use beyond the size scaling of moore's Law. A major obstacle has been achieving control of the spin variable at temperatures required for practical applications. Here we demonstrate electrical injection, detection and precession of spin accumulation in silicon, the cornerstone material of device technology, at temperatures that easily exceed these requirements. We observe Hanle precession of electron spin accumulation in silicon for a wide range of bias, show that the magnitude of the Hanle signal agrees well with theory, and that the spin lifetime varies with silicon carrier density. These results confirm spin accumulation in the silicon transport channel to 500 K rather than trapping in localized interface states, and enable utilization of the spin variable in practical device applications.

Abstract-We demonstrate that information can be transmitted and processed with pure spin currents in silicon. Fe/ Al2O3 tunnel barrier contacts are used to produce significant electron spin polarization in the silicon, generating a spin current which flows outside of the charge current path. The spin orientation of this pure spin current is controlled in one of three ways: (a) by switching the magnetization of the Fe contact, (b) by changing the polarity of the bias on the Fe/Al2O3 "injector" contact, which enables the generation of either majority or minority spin populations in the Si, providing a way to electrically manipulate the injected spin orientation without changing the magnetization of the contact itself, and (c) by inducing spin precession through application of a small perpendicular magnetic field. Spin polarization by electrical extraction is as effective as that achieved by the more common electrical spin injection. The output characteristics of a planar silicon three terminal device are very similar to those of nonvolatile giant magnetoresistance metal spin-valve structures.

Ferronlagnetic semiconductors (FMS) provide unpmzedented opportunity ro comrol spindependent behavior in semiconductor device heterostructurer. Although much eftort hits focused on Ill-Mn-V materials such as GaMnAs. the mechanism of ferroinagnetic order remains UIICI~:IP, Particularly the precise roles played hy the dopant and the semiconductor host. The success of the epitaxial growth of the FMS Mn,Cel., [I] ha< motivated our eftortr to extend the Ge-hased

Magnetoelectronics refers t o n new class of devices that utilize the intrinsic spin exhibited by electmns and holes to offer new functionality and performance in semiconductor heterostructures. Realization of future semiconductor spintronic devices such as the spin-PET, resonant tunneling diode and spin polarized light emitting diode (spin-LED) will require efficient electrical injection of spin-polarized carriers from a contact into a Emiconductor. We report here that spin injection from an Fe Schottky CUntBCt pnnfuces B spin polarization of 32% in an AICitAs/C,tAs quamum well, demonstrate via the Rowell criteria that tunneling is the dominant transport process, and exanlinc the atomic structure of the spin injecting interface with TEM.Ferromagnetic metals are attractive BR spin injecting contacts because they offer high Curie temperatures. a snurce of spin polarized electroin, and enjoy a very high level of material development due to their widespread use in magnetic recording technology.However, theory indicates that for intimate metel/semiconductur contitcts only very smiill effects (4.01%) can be expecled i l t h e carriers are conducted acmsb the interlace in the diffusive transport regime [I]. I t has k e n shown that this ohstack can he overcome if a tunnel harricr is used to control Rcccnt cxpcrimcnt;d cflorts reponed spin injection from an Fe Schottky contact into a GaAs-based LED which produced a spin polarization of 2% in the semiconductor L31 and allribulcd this to tunneling, Previously, wc succcssfully injected spin from an Fe contact into an AlGaAslGaAs LED structure and obtaincd electron spin polarizations of 138 in the GaAs quantum well [4]. Thc circular poliirirsilian of the surface-emitted light provides a direct measure of the carrier spin polarization. We repon here our most recent results which include an increase of this polarization to 32%. by the electronic and atolnic structure ollhal interface. In this study we have tailored the Schottky barrier which forms at the FeIAIGaAs interface with the intent of optimizing the tunneling process. Figure I shows a schematic diagram of the structure of the spin-LEDs Quantum Well Fig. I. a) Schematic diagram and b) flat band diagram u f Schottky barrier in spin-LED Thc cfficicncy of spin injcction across a hctcmintcrkcc can bc strongly affcctcd u x d in this study aid thc corrcsponding flat band diagram. Thc Schottky barricr provides B natural tuiiiiel barrier for injection of spin-polarized elr~trons from thc metal contiid intu the quantum well heterurtruclurc. The width of the depletion rcgion near the Fe/AIGaAr interface. and hence the effective shape of the tunnel barrier, i s controlled by the semiconductor dmiae ~rufile during MBE growth. . . . . . . -. .measurenlents show m atomically abrupt interface (Pig. 2). We have applied the three Rowell criteria In analyie the electrical tramport process, nnd conclude that tunneling dominates. Figure 1 shows the A t tcmpcrilturc d&idcncc ofthc zero-bias resistance through the Schottky tunnel barrier. A...

Efficient electricill injection, transport and manipulation of spin-polarized cxricrs in a Eemiconductor are essential requirements for utiliring the spin degree of freedom in future electronic dcviccs. Feiromagnetic semiconductors (FMSs) are promising candidates in this effort F i n e their exchange split band edges offer both spin injection and spin-selective transport in substrate is especially attractive basis for high frequency, IOWheterostructures. An fl-type FMS which cm be epitaxially grown on a device quality because electron tranapurt i s the power operation. demonstr;acd cpitaxiid growth 0.4 Field (T) of wtype CdCr,Se,. a chalcogenide spinel FMS, on GaAs(W1) and GaP(001) 111. O2 Samples grown by molecular beam epitaxy are single crystal 0 despite a lattice mismatch of 0 50 100 150 200 250 300 350 1.7% with Gap and S.2% withGaAs. Cross-sectional TEM imeges reveal that the CdCr,Sc, gmwth appears to microcrystals with slight miaaricniations rclstive to AIGaAs. consistent with the lattice mismatch. Temperature dependcnt transport data show that thc films arc scmiconducting in charactcr. arc n-typc as grown, and havc room temperature carrier concentrations of n -10" cni'. T~C magnetic properties, shown in Fig. I, are similar to that of hulk CdCrSe,. Filmq exhihit hysteretic hehavior with significant remanence. an in-plane easy axis with acoercive field of -I 25 Oe and a Curie temmrature of 130 K. Rcccnlly, wc -0.2 0 0.2 Temperature (K) Fig. I. Nolmalized msgne1iz;rtion vs. temperature of epitaxially grown CdCr2Sc4. h c f shows the magnetization vs applied field at S K. devices. To this end. we have performed measurements of hand offsets and spin transport in CdCr,SeJAIGaAslGaAs l i e t e r~~l i ~~cturcs. heterojwictions w e mcasured to high rwnlution hy internal photoemission (IPE) using a widely tunablc optical psranietl-ic 1 I Thc hmd dkconlinuitics of CdCr,ScJ(AIG;!)As and CdCr,ScJZnSc amplifier system. The conduction band (CB) offset AE< = 650 meV at the CdCr2Se,-AI , , , , Ga ,,,", As interface i s determined from the threshold energy of the pliotocurrcnt spcctrum at room temperstu1e (wee Figurc 2). Elcclrvna iiijcctcd into energy, which may Photon " 9 " lev1 cause strong electron scattering in the latticc and a Fig. 2. Internal phatoemisqion spectrum from an unhiascd CdCr~Se~l(AIGa)A~ helerujunclion tit room temperature. The insetc show the cross section ofthe LED and the band corresponding reduction in spin align'1mt. Dolarizalion. Initial result\ on electrical spin iniectivn from spin-LED stru~tures re~eal . . defect-dominated electroluminescence. in which ?pin information i s known 10 he lost as rcportcd for ZnMnScIAIGaAs LEDs 121.CdCI-,Sc~,,Sc/(AIF;I)As hctcrostructurcs. thus incrciaing thc dianccs for spin injection into the GaA-QW. IPE ieasureineiits indicate ii CB offW AE, = 530 meV at the CdCr,Se,-ZnSc interface. Initial spin injection studies show that this reduccd CB offsct is enough to facilitate measurahle spin injection efficiencies from the CdCr,Se, into 811AlGaAsiGaAs spin-LED. producin...