P.E. Thompson

United States Naval Research Laboratory, Washington, Washington, D.C., United States

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Publications (100)131.91 Total impact

  • Acta Materialia 02/2014; 65:418-424. DOI:10.1016/j.actamat.2013.11.011 · 3.94 Impact Factor
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    ABSTRACT: We report on spin injection experiments at Fe/MgO/Si interfaces using all electrical injection and detection. MgO is a promising magnetic tunnel junction material, and its incorporation with Si-based spintronics has only recently been reported in degenerately doped Si (n ˜10^20 cm-3) [1]. We focus here on spin accumulation under the injecting contact for much lower n-doping levels by measuring the Hanle effect in a standard 3-terminal scheme where injection and detection are done using the same contact. The Fe/MgO spin injector was sputter deposited onto various n-doped Si bulk substrates using a variety of different substrate temperatures. The best tunnel barriers were obtained when the MgO was deposited at 70^oC and annealed in-situ before Fe deposition. Fits to Hanle curves using the drift-diffusion model for Si samples with n=4x10^18 cm-3 yield spin lifetimes taus = 0.28 ns up to 30 K and a spin diffusion length Ls=&surd;Dtaus of 0.65 mum (the diffusion constant D is obtained from the mobility assuming degenerate statistics). We determine the dependence on n, and comment on the potential differences between SOI and bulk Si wafer transport channels. [1] T. Sasaki, et al., Appl. Phys. Exp. 2 (2009).
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    ABSTRACT: We analyze the circular polarization (Pcirc) of the electroluminescence (EL) from Si-based spin-LEDs using a recent theory [1] which provides a quantitative relation between the polarization of phonon-assisted optical transitions measured in the EL, and the electron spin polarization electrically injected from Fe/Al2O3 and Fe/SiO2 tunnel barrier contacts [2,3]. EL spectra include features due to transverse acoustic (TA) and transverse optical (TO) phonon-mediated recombination occurring in the p-doped (p˜10^19cm-3) substrate. Pcirc of 3.5% is typical for the TA at 5K, and is systematically higher than that of the TO by a factor ˜1.7, consistent with theory. The maximum polarization predicted for the TA is 13% for recombination of 100% polarized electrons in p-type Si (10^19cm-3). Thus the measured Pcirc 3.5% corresponds to an electron spin polarization (Pspin) of 27% produced by electrical injection from our tunnel barrier contacts. A similar analysis applied to the TO phonon at 80K yields Pspin of 25%. Thus the theory enables quantitative interpretation of optical polarization in indirect gap semiconductors, facilitating future studies of spin injection. [1] P. Li and H. Dery, Phys. Rev. Lett. 105, 037204 (2010). [2] B.T. Jonker, et al., Nature Physics 3, 542 (2007). [3] C.H. Li, et al, Appl. Phys. Lett. 95, 172102 (2009).
  • MRS Online Proceeding Library 01/2011; 533. DOI:10.1557/PROC-533-367
  • MRS Online Proceeding Library 01/2011; 216. DOI:10.1557/PROC-216-259
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    ABSTRACT: We have demonstrated the injection, modulation and detection of pure spin diffusion current in silicon in a lateral transport geometry compatible with existing device design, fabrication and scaling. This approach injects spin-polarized electrons near the silicon conduction band edge with near unity conversion efficiency and low bias voltages (~ 2 eV) compatible with CMOS technology.
    Electron Devices Meeting (IEDM), 2009 IEEE International; 01/2010
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    ABSTRACT: Whereas spin injection from a ferromagnet into heavily doped Si is facilitated by tunneling through a narrow depletion region, it is shown here that for moderately doped Si it is crucial to suppress the Schottky barrier. Reducing carrier depletion by exposing the Si surface to a Cs flux prior to Al2O3 tunnel barrier growth, we demonstrate spin injection by tunneling from Fe into Si (confirmed by circular polarized electroluminescence) and achieve electrical detection (via the Hanle effect) of spin accumulation induced at room temperature in Ni80Fe20/Al2O3/Si junctions with 1.5×1018 cm−3 carrier density. Tailored interfaces thus enable spin injection into moderately doped Si.
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    ABSTRACT: Phosphorus doping of silicon during growth by molecular beam epitaxy (MBE) has been investigated in the temperature regime 700°C to 870°C. By designing a growth sequence that fully accounts for the P deposited in a delta-doped layer, and then tracks the P as it segregates into the undoped Si and traps the surface P in a low temperature Si cap, it was determined that the onset of significant P evaporation during growth occurred at a substrate temperature of 663°C±10°C. The P sublimation process had an activation energy of 199kJ/mol±22kJ/mol.
    Thin Solid Films 01/2010; 518(6). DOI:10.1016/j.tsf.2009.10.105 · 1.87 Impact Factor
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    ABSTRACT: We demonstrate that information can be transmitted and processed with pure spin currents in silicon. Fe/Al<sub>2</sub>O<sub>3</sub> 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: 1) by switching the magnetization of the Fe contact; 2) by changing the polarity of the bias on the Fe/Al<sub>2</sub>O<sub>3</sub> "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 3) by inducing spin precession through the 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.
    IEEE Transactions on Electron Devices 11/2009; DOI:10.1109/TED.2009.2027975 · 2.36 Impact Factor
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    ABSTRACT: We demonstrate spin polarized tunneling from Fe through a SiO2 tunnel barrier into a Si n-i-p heterostructure. Transport measurements indicate that single step tunneling is the dominant transport mechanism. The circular polarization, Pcirc, of the electroluminescence (EL) shows that the tunneling spin polarization reflects Fe majority spin. Pcirc tracks the Fe magnetization, confirming that the spin-polarized electrons radiatively recombining in the Si originate from the Fe. A rate equation analysis provides a lower bound of 30% for the electron spin polarization in the Si at 5 K. Comment: to appear in Appl. Phys. Lett. Oct. 26, 2009
    Applied Physics Letters 10/2009; 95(17). DOI:10.1063/1.3254228 · 3.52 Impact Factor
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    ABSTRACT: Robust Si resonant interband tunnel diodes have been designed and tested that demonstrate as-grown negative differential resistance at room temperature with peak-to-valley current ratios (PVCR) up to 2.5 and peak current densities in the order of 1 kA/cm<sup>2</sup>. The as-grown Si p<sup>+</sup>in<sup>+</sup> structures were synthesised using solid source molecular beam epitaxy, incorporating B and P delta-doped layers. Both structures have shown thermal stability after 1 min post-growth anneals up through 675degC and the PVCR improves to 2.8 for a 575degC 1 min anneal.
    Electronics Letters 08/2009; DOI:10.1049/el.2009.1007 · 1.07 Impact Factor
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    ABSTRACT: We compare electrical spin injection from Fe into Si n-i-p heterostructures using different tunnel barriers—a reversed biased Fe/Si Schottky contact and a Fe / Al <sub>2</sub> O <sub>3</sub> barrier. The electroluminescence (EL) spectra are dominated by transverse acoustic and optical phonon emission for both types of structures. The circular polarization of the EL tracks the Fe magnetization, confirming that the spin-polarized electrons originate from the Fe in each case. However, the polarization is lower for the Fe/Si contact than for the Fe / Al <sub>2</sub> O <sub>3</sub> contact. Transmission electron microscopy reveals a complex interface and intermixing for Fe/Si that is absent in Fe / Al <sub>2</sub> O <sub>3</sub>/ Si .
    Applied Physics Letters 04/2009; DOI:10.1063/1.3099049 · 3.52 Impact Factor
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    ABSTRACT: Strain-engineered Si-based resonant interband tunneling diodes grown on commercially available Si<sub>0.8</sub>Ge<sub>0.2</sub> virtual substrates were developed that address issues of P dopant diffusion and electron confinement. Strain-induced band offsets were effectively utilized to improve tunnel diode performance versus the control device, particularly the peak-to-valley current ratio (PVCR). By growing tensilely strained Si layers cladding the P delta-doping plane, the quantum well formed by the P delta-doping plane is deepened, which concurrently increases the optimal annealing temperature from 800 to 835 and facilitates an increase in the PVCR up to 1.8times from 1.6 to 2.8 at room temperature, which is significantly better than previous results on strained substrates.
    IEEE Electron Device Letters 07/2008; DOI:10.1109/LED.2008.923208 · 3.02 Impact Factor
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    ABSTRACT: We have recently demonstrated successful electrical injection of spin-polarized electrons from an Fe film through an Al2O3 tunnel barrier into Si [1]. The spin polarization in the Si is ˜30% at 5K, with significant polarization sustained to at least 125K. In this study we compare electrical spin injection from Fe into MBE grown Si n-i-p heterostructures using different tunnel barriers- a reversed biased Fe/Si Schottky contact and an Fe/Al2O3 barrier. For both types of structures the electroluminescence (EL) spectra are dominated by transverse acoustic and optical phonon emissions in the Si. The surface emitted circular polarization of the EL due to radiative recombination in the Si tracks the Fe magnetization, confirming that the spin-polarized electrons originate from the Fe for both types of samples. However, the polarization is lower for the Fe/Si contact than that of the Fe/Al2O3/Si system. Systematic TEM analysis has been performed to correlate the interface structure with the observed optical polarization, and reveals some Fe/Si intermixing which is absent in the Fe/ Al2O3/Si structure. [1] B.T. Jonker et al., Nature Physics 3, 542 (2007). This work was supported by ONR and core programs at NRL.
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    ABSTRACT: This study reports a Si RITD whose characteristics improve with increasing anneal time, resulting in a peak current density (J<sub>P</sub>) and PVCR up to 2.97 kA/cm<sup>2</sup> and 3.08, respectively.
    Semiconductor Device Research Symposium, 2007 International; 01/2008
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    ABSTRACT: A driving force in electronic device research has been increased functionality with reduced energy loss. One of the techniques proposed for meeting these goals has been the employment of tunnel diodes integrated with conventional transistors to form logic and memory circuits. Considerable progress has been made in the area of Si-based resonant interband tunnel diodes (RITD).
    Semiconductor Device Research Symposium, 2007 International; 01/2008
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    ABSTRACT: We present the electrical injection, detection, and magnetic field modulation of lateral diffusive spin transport through silicon using surface contacts. Fe/Al2O3 tunnel barrier contacts are used to create and analyze the flow of pure spin current in a silicon transport channel. Nonlocal detection techniques show that the spin current detected after transport through the silicon is sensitive to the relative orientation of the magnetization of the injecting and detecting contacts. Hanle effect measurements demonstrate that the spin current can be modulated by a perpendicular magnetic field, which causes the spin to precess and dephase in the transport channel.
    Applied Physics Letters 11/2007; 91(21):212109-212109-3. DOI:10.1063/1.2817747 · 3.52 Impact Factor
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    ABSTRACT: We report the first directly-measured sensitivity performance of a zero-bias Si-based heterojunction backward detector, which is readily compatible with mainstream silicon technology. A measured sensitivity of 2376 V/W driven from a 50 Omega source at zero-bias has been obtained. A cutoff frequency of 1.8 GHz was extracted with a series resistance of 290 Omega and a junction capacitance of 0.307 pF using a small signal model established to fit the measured S-parameters for a 5 mum diameter mesa device.
    Device Research Conference, 2007 65th Annual; 07/2007
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    ABSTRACT: A method is investigated to directly engineer the voltage swing in SiGe resonant interband tunnel diodes (RITDs). Voltage swing, defined here as the voltage difference between the peak voltage and the projected peak voltage, is independent of series resistance, and thus directly impacts the noise margin in hybrid tunnel diode memory and logic applications. The three components of the total RITD current are analyzed to describe the voltage swing. The dependence of voltage swing on delta-doping concentrations and post-growth annealing temperatures in SiGe RITDs grown by low-temperature molecular beam epitaxy (LT-MBE) is investigated and the experimental results are compared with a theoretical analysis. Techniques to increase the voltage swing are discussed
    IEEE Transactions on Nanotechnology 04/2007; DOI:10.1109/TNANO.2007.891831 · 1.62 Impact Factor
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    ABSTRACT: Si-based resonant interband tunneling diodes (RITD) with spacer thicknesses varying from 1 to 16 nm were grown and fabricated. The effect of spacer thickness on the peak-to-valley current ratio (PVCR), peak current density J<sub>p</sub>, and voltage swing was studied. By increasing the tunneling spacer thickness up to 16 nm, RITDs with a J <sub>p</sub> of as low as 20 mA/cm<sup>2</sup> with an associated PVCR of 1.6 were obtained, which are suitable for low-power tunnel diode SRAM applications. With the previously reported highest RITD J<sub>p</sub> of 218 kA/cm<sup>2</sup>, a J<sub>p</sub> spanning nearly seven orders of magnitude can be obtained by engineering the tunneling spacer thickness and doping densities, thus demonstrating tremendous flexibility to optimize J<sub>p</sub> for different circuit applications (logic, memory, and mixed-signal). Using a low-current-density RITD developed in this paper, a bread-boarded one-transistor tunneling-based SRAM (TSRAM) memory cell with low standby power consumption was demonstrated. This is the first report of a Si-based TSRAM memory circuit using Si-based RITDs. The result demonstrates the potential of Si-based tunnel diodes for low-power memory applications
    IEEE Transactions on Electron Devices 10/2006; DOI:10.1109/TED.2006.879678 · 2.36 Impact Factor

Publication Stats

859 Citations
131.91 Total Impact Points

Institutions

  • 2010
    • United States Naval Research Laboratory
      Washington, Washington, D.C., United States
  • 2002–2007
    • The Ohio State University
      • • Department of Electrical and Computer Engineering
      • • Department of Physics
      Columbus, OH, United States
  • 2001–2006
    • Rochester Institute of Technology
      • Department of Electrical and Microelectronic Engineering
      Rochester, NY, United States
  • 2000–2001
    • University of Delaware
      • Department of Electrical and Computer Engineering
      Delaware, United States
  • 1996–1997
    • Northrop Grumman
      Falls Church, Virginia, United States
  • 1995
    • Wright-Patterson Air Force Base
      Dayton, Ohio, United States