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Efficient spin injection into silicon and the role of the Schottky barrier.

Dankert A, Dulal RS, Dash SP - Sci Rep (2013)

Bottom Line: Implementing spin functionalities in Si, and understanding the fundamental processes of spin injection and detection, are the main challenges in spintronics.This dramatic change in the spin injection and detection processes with increased Schottky barrier resistance may be due to a decoupling of the spins in the interface states from the bulk band of Si, yielding a transition from a direct to a localized state assisted tunneling.Our study provides a deeper insight into the spin transport phenomenon, which should be considered for electrical spin injection into any semiconductor.

View Article: PubMed Central - PubMed

Affiliation: Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden.

ABSTRACT
Implementing spin functionalities in Si, and understanding the fundamental processes of spin injection and detection, are the main challenges in spintronics. Here we demonstrate large spin polarizations at room temperature, 34% in n-type and 10% in p-type degenerate Si bands, using a narrow Schottky and a SiO2 tunnel barrier in a direct tunneling regime. Furthermore, by increasing the width of the Schottky barrier in non-degenerate p-type Si, we observed a systematic sign reversal of the Hanle signal in the low bias regime. This dramatic change in the spin injection and detection processes with increased Schottky barrier resistance may be due to a decoupling of the spins in the interface states from the bulk band of Si, yielding a transition from a direct to a localized state assisted tunneling. Our study provides a deeper insight into the spin transport phenomenon, which should be considered for electrical spin injection into any semiconductor.

No MeSH data available.


Related in: MedlinePlus

Temperature dependence of the spin signal for degenerate n-type Si.Measurements are shown for two different devices. (a) Hanle spin signal at 5 K and 300 K for an applied bias voltage of +0.2 V (b) Temperature dependence of spin-RA at an applied bias voltage of +0.2 V. The lines represent the theoretical prediction for spin accumulations created through direct tunneling: 28. (c) Temperature dependence of the effective spin lifetime (error bars are smaller than data points).
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f3: Temperature dependence of the spin signal for degenerate n-type Si.Measurements are shown for two different devices. (a) Hanle spin signal at 5 K and 300 K for an applied bias voltage of +0.2 V (b) Temperature dependence of spin-RA at an applied bias voltage of +0.2 V. The lines represent the theoretical prediction for spin accumulations created through direct tunneling: 28. (c) Temperature dependence of the effective spin lifetime (error bars are smaller than data points).

Mentions: The spin-resistance-area product () is found to be in the range 1–4 kΩμm2 (Fig. 2b), which is large, compared to theoretical predictions430. In the diffusive regime, RSA should be equal to P2ρSiLsd = 10 Ωμm2, where ρSi = 3 mΩcm at 300 K, and Lsd is the spin diffusion length4. Although the experimental values are large, we can rule out any enhancement of the spin signal by tunneling through localized states over the full temperature range. The weak temperature dependence of the Hanle spin signal (Fig. 3a) and RSA (Fig. 3b) at low bias voltages matches the theoretical predictions 728. This indicates a true spin accumulation in the Si conduction band over the full temperature range, since localized interface states are expected to provide a larger temperature dependence of RSA2231. The thinner, low resistance Schottky barrier of this highly doped n++ Si devices couples well the localized states and the Si conduction band allowing for direct spin-polarized tunneling1423. It should also be noted that the weak temperature dependence of SiO2 has an advantage over other oxide tunnel barriers such as Al2O34 and MgO1331, in which RSA increases exponentially at lower temperatures. Such low temperature dependence of spin signal has also been reported using plasma SiO2 tunnel barriers on Si12. From the separately measured diffusion constant and the Lorentzian fitting of the Hanle curves, the lower limit for the spin lifetime and the spin diffusion length are found to be and , respectively, at room temperature. These values match very well previously reports for such highly doped Si at room temperature71832. Furthermore, the spin lifetime is found to be independent of both temperature and bias voltage (Fig. 2c and 3c), supporting the direct tunneling and detection of spin accumulations in the bulk Si conduction band over the measured temperature and bias voltage ranges.


Efficient spin injection into silicon and the role of the Schottky barrier.

Dankert A, Dulal RS, Dash SP - Sci Rep (2013)

Temperature dependence of the spin signal for degenerate n-type Si.Measurements are shown for two different devices. (a) Hanle spin signal at 5 K and 300 K for an applied bias voltage of +0.2 V (b) Temperature dependence of spin-RA at an applied bias voltage of +0.2 V. The lines represent the theoretical prediction for spin accumulations created through direct tunneling: 28. (c) Temperature dependence of the effective spin lifetime (error bars are smaller than data points).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3824168&req=5

f3: Temperature dependence of the spin signal for degenerate n-type Si.Measurements are shown for two different devices. (a) Hanle spin signal at 5 K and 300 K for an applied bias voltage of +0.2 V (b) Temperature dependence of spin-RA at an applied bias voltage of +0.2 V. The lines represent the theoretical prediction for spin accumulations created through direct tunneling: 28. (c) Temperature dependence of the effective spin lifetime (error bars are smaller than data points).
Mentions: The spin-resistance-area product () is found to be in the range 1–4 kΩμm2 (Fig. 2b), which is large, compared to theoretical predictions430. In the diffusive regime, RSA should be equal to P2ρSiLsd = 10 Ωμm2, where ρSi = 3 mΩcm at 300 K, and Lsd is the spin diffusion length4. Although the experimental values are large, we can rule out any enhancement of the spin signal by tunneling through localized states over the full temperature range. The weak temperature dependence of the Hanle spin signal (Fig. 3a) and RSA (Fig. 3b) at low bias voltages matches the theoretical predictions 728. This indicates a true spin accumulation in the Si conduction band over the full temperature range, since localized interface states are expected to provide a larger temperature dependence of RSA2231. The thinner, low resistance Schottky barrier of this highly doped n++ Si devices couples well the localized states and the Si conduction band allowing for direct spin-polarized tunneling1423. It should also be noted that the weak temperature dependence of SiO2 has an advantage over other oxide tunnel barriers such as Al2O34 and MgO1331, in which RSA increases exponentially at lower temperatures. Such low temperature dependence of spin signal has also been reported using plasma SiO2 tunnel barriers on Si12. From the separately measured diffusion constant and the Lorentzian fitting of the Hanle curves, the lower limit for the spin lifetime and the spin diffusion length are found to be and , respectively, at room temperature. These values match very well previously reports for such highly doped Si at room temperature71832. Furthermore, the spin lifetime is found to be independent of both temperature and bias voltage (Fig. 2c and 3c), supporting the direct tunneling and detection of spin accumulations in the bulk Si conduction band over the measured temperature and bias voltage ranges.

Bottom Line: Implementing spin functionalities in Si, and understanding the fundamental processes of spin injection and detection, are the main challenges in spintronics.This dramatic change in the spin injection and detection processes with increased Schottky barrier resistance may be due to a decoupling of the spins in the interface states from the bulk band of Si, yielding a transition from a direct to a localized state assisted tunneling.Our study provides a deeper insight into the spin transport phenomenon, which should be considered for electrical spin injection into any semiconductor.

View Article: PubMed Central - PubMed

Affiliation: Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden.

ABSTRACT
Implementing spin functionalities in Si, and understanding the fundamental processes of spin injection and detection, are the main challenges in spintronics. Here we demonstrate large spin polarizations at room temperature, 34% in n-type and 10% in p-type degenerate Si bands, using a narrow Schottky and a SiO2 tunnel barrier in a direct tunneling regime. Furthermore, by increasing the width of the Schottky barrier in non-degenerate p-type Si, we observed a systematic sign reversal of the Hanle signal in the low bias regime. This dramatic change in the spin injection and detection processes with increased Schottky barrier resistance may be due to a decoupling of the spins in the interface states from the bulk band of Si, yielding a transition from a direct to a localized state assisted tunneling. Our study provides a deeper insight into the spin transport phenomenon, which should be considered for electrical spin injection into any semiconductor.

No MeSH data available.


Related in: MedlinePlus