The control and manipulation of the electron spin in semiconductors is central to spintronics1,2, which aims to represent digital information using spin orientation rather than electron charge. Such spin-based technologies may have a profound impact on nanoelectronics, data storage, and logic and computer architectures.
Recently it has become possible to induce and detect spin
polarization in otherwise non-magnetic semiconductors (gallium arsenide and silicon) using all-electrical structures3–9, but so far only at temperatures below 150K and in n-type materials, which limits further development. Here we demonstrate room-temperature electrical
injection of spin polarization into n-type and p-type silicon from a ferromagnetic tunnel contact, spin manipulation using the Hanle effect and the electrical detection of the induced spin accumulation.
A spin splitting as large as 2.9meV is created in n-type
silicon, corresponding to an electron spin polarization of 4.6%. The extracted spin lifetime is greater than 140 ps for conduction electrons in heavily doped n-type silicon at 300K and greater than 270 ps for holes in heavily doped p-type silicon at the same temperature.
The spin diffusion length is greater than 230nmfor electrons
and 310nm for holes in the corresponding materials. These results open the way to the implementation of spin functionality in complementary silicon devices and electronic circuits operating at ambient temperature, and to the exploration of their prospects and the fundamental rules that govern their behaviour.

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Electrical creation of spin polarization in silicon at room temperature

A review is presented of the recent advances in the study of oxygen precipitation and of the main properties of oxide precipitates in silicon. After a general overview of the system ‘‘oxygen in silicon,’’ the thermodynamics and the kinetics of the precipitate formation are treated in detail, with major emphasis on the phenomenology; subsequently, the most important techniques for the characterization of the precipitates are illustrated together with the most interesting and recent results. Finally, the possible influence of oxygen precipitation on technological applications is stressed, with particular attention to recent results regarding device yield. Actually, the essential novelty of this review rests on the attempt to give an extended picture of what has been recently clarified by means of highly sophisticated diagnostic methods and of the influence of precipitation on the properties of semiconductor devices.

Oxygen precipitation in silicon

The formation of supersaturated substitutional alloys by ion implantation and rapid liquid‐phase‐epitaxial regrowth induced by pulsed laser annealing has been studied using Rutherford backscattering, ion channeling analysis. Group‐III (Ga, In) and group‐V (As, Sb, Bi) dopants have been implanted into single‐crystal silicon at doses ranging from 1×1015 to 1×1017/cm2. The samples were annealed with a Q‐switched ruby laser (energy density ∼1.5 J/cm2, pulse duration ∼15×10−9 sec). Ion channeling analysis shows that laser annealing incorporates these dopants into substitutional lattice sites at concentrations far in excess of the equilibrium solid solubility. Channeling measurements indicate the silicon crystal is essentially defect free after laser annealing. Also values for the maximum dopant concentration (Cmaxs) that can be incorporated into substitutional lattice sites are determined for our annealing conditions. Dopant profiles determined by Rutherford backscattering are compared to model calculations wh...

Supersaturated substitutional alloys formed by ion implantation and pulsed laser annealing of group-III and group-V dopants in silicon

Silicon single crystals are grown by the Czochralski method with a variety of growth rates and rotation rates. Segregation coefficients of impurities are found to depend on the growth conditions as is expected by the existing theory. Diffusion coefficients of impurities in silicon melt are determined for B, Al, Ga, In, P, As and Sb. Diffusion coefficients of group V impurities are found to increase as the tetrahedral covalent radius of the impurity atom decreases. In the case of group III impurities, the dependence of diffusion coefficients on the tetrahedral covalent radius is not so clear as in the case of group V impurities.

Diffusion Coefficients of Impurities in Silicon Melt

A synthesis is given of the most significant experimental features of the semiconductor-to-metal transition in group IV semiconductors. Two characteristic concentrations are discussed, the first being for a delocalization of electrons (the "Mott" transition), and the second being associated with the entry of the Fermi level into the conduction band of the host material. Experimental values are given for the two concentrations in several materials. Experimental data covering measurements of Hall coefficient, electrical resistivity and carrier mobility, NMR properties, magnetoresistance, magnetic susceptibility, and ESR properties are employed in arriving at values for the two characteristic concentrations. Si: P is taken as the model system because of the completeness of experimental measurements. Si: As is also briefly considered. Existing data for $n$-Ge are examined, as well as the more restricted evidence concerning $n$-SiC.

Semiconductor-to-Metal Transition in n -Type Group IV Semiconductors

Dyson effect was investigated in the electron spin resonance of phosphorus doped silicon to know the dynamical characteristics of the paramagnetic center responsible for the single adsorption line around g -value of 2. Experiments were carried out at room, liquid nitrogen and liquid helium temperatures using samples of rod shape containing phosphorus atoms about 10 17 , 10 18 and 10 19 cm -3 . Theoretical line shape was calculated to simulate the effect of parameters such as sample thickness, skin depth and diffusion time of electrons through the skin depth. The observed absorption line showed distortion consistent with the Dyson theory. The diffusion time was estimated to be several times of the electron spin relaxation time. Comparing with the diffusion time calculated from the electron mobility, a model is proposed that there might be two types of electron motion, namely rapid motion in an impurity cluster and slow transitions among the clusters.

Dyson Effect in the Electron Spin Resonance of Phosphorus Doped Silicon

Electron spin resonance experiments were carried out at room and liquid nitrogen temperatures on n -type silicon doped with various amounts of phosphorus. A single absorption line was observed, its g -value and line width being functions of the donor concentration. At room temperature, the g -value and line width vary monotonically with the donor concentration, while at liquid nitrogen temperature, these resonance parameters change their dependence at a certain donor concentration. The change in the behavior was considered to have a connection with the transition from localized to nonlocalized state, the onset of degeneracy and impurity band conduction. The experimental results were analyzed by the existing theories of the electron spin resonance of conduction electrons. Qualitative agreement with the theory was found, which would be a confirmation of the model that the observed electron spin resonance is related with the electrical conduction.

Effect of Doping on the Electron Spin Resonance in Phosphorus Doped Silicon. II

Growth of heavily doped germanium and silicon crystals is investigated from the standpoint of constitutional supercooling. When the impurity concentration exceeds a certain value, corrugations appear on the crystal surface. The impurity concentration necessary for the appearance of the corrugation, the doping limit, is determined for various impurity elements. The analysis of the experimental results shows that definite magnitude of supercooling is required for the irregular growth of crystals which gives rise to corrugations on the crystal surface and results in the formation of polycrystals.

Constitutional Supercooling during the Crystal Growth of Germanium and Silicon

Absorption intensity of the electron spin resonance in phosphorus doped silicon was measured at room and liquid nitrogen temperatures by comparing with signal from the known amount of DPPH. Experimental conditions were devised so as to locate the silicon sample and DPPH at the position of RF magnetic field of the same strength. The absorption intensity was measured as a function of the electron or phosphorus concentration and compared with the theoretical calculation based on the paramagnetic susceptibility of conduction electrons. At room temperature, the observed intensity was found to agree quite well with the theoretical calculation, showing that the electron spin resonance originates from conduction electrons. At liquid nitrogen temperature, however, qualitative agreement with the theoretical calculation was found only at higher donor concentration.

Hiroshi Kodera

Papers

Diffusion Coefficients of Impurities in Silicon Melt

Dyson Effect in the Electron Spin Resonance of Phosphorus Doped Silicon

Effect of Doping on the Electron Spin Resonance in Phosphorus Doped Silicon. II

Constitutional Supercooling during the Crystal Growth of Germanium and Silicon

Effect of Doping on the Electron Spin Resonance in Phosphorus Doped Silicon. III. Absorption Intensity