Reduction of Spin Injection Efficiency by Interface Defect Spin Scattering in $\mathrm{Z}\mathrm{n}\mathrm{M}\mathrm{n}\mathrm{S}\mathrm{e}/\mathrm{A}\mathrm{l}\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}\mathrm{\text{−}}\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ Spin-Polarized Light-Emitting Diodes

We report the first experimental demonstration that interface microstructure limits diffusive electrical spin-injection efficiency across heteroepitaxial interfaces. An inverse correlation between spin-polarized electron injection efficiency and interface defect density is demonstrated for $\mathrm{Z}\mathrm{n}\mathrm{M}\mathrm{n}\mathrm{S}\mathrm{e}/\mathrm{A}\mathrm{l}\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}\mathrm{\text{−}}\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ spin-polarized light-emitting diodes that exhibit quantum well spin polarizations up to 85%. A theoretical treatment shows that the suppression of spin injection due to interface defects results from the contribution of the defect potential to the spin-orbit interaction, which increases the spin-flip scattering.

Figure 1

Schematic of the $\mathrm{Z}\mathrm{n}\mathrm{M}\mathrm{n}\mathrm{S}\mathrm{e}/\mathrm{A}\mathrm{l}\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}\mathrm{\text{−}}\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ spin-LED. Spin-polarized electrons are injected across the ZnMnSe-AlGaAs interface into the GaAs quantum well. Radiative recombination in the QW results in circularly polarized light emission.

Figure 2

Dark-field cross-sectional transmission electron micrograph of a ZnMnSe spin-LED. Stacking faults in $⟨111⟩$ directions are observed to nucleate at the ZnMnSe-AlGaAs interface. This sample had a stacking fault concentration of $9\times {10}^4{\mathrm{c}\mathrm{m}}^{-1}$ and spin-injection efficiency of 49%.

Figure 3

Correlation of quantum well (QW) spin polarization with stacking fault density. Two data points nearly overlap at 85% polarization. The error bars are comparable to the symbol size. The dashed line is the calculated result from Eq. (5) and has no adjustable parameters.

Figure 4

Diagram illustrating the linear interface defects resulting from the intercept of (111)-type SF planes and the interface plane. Only one of the four possible (111)-type SF planes is shown for clarity.

Figure 5

Angular distributions of the spin polarization about the axis of the linear interface defect (the [110] direction) for different values of $k{r}_0$ following scattering from the defect. The outer dashed circle corresponds to 100% spin polarization, while the inner circle divides the regions of the negative and positive polarizations. The dipole moment is oriented along the [110] direction, i.e., in the interface plane. Spin-flip scattering dominates for all electrons in the forward direction (towards the GaAs quantum well).