Spin-polarized tunneling through a diluted magnetic semiconductor quantum dot

Spin-polarized tunneling through a diluted magnetic semiconductor quantum dot embedded in a tunneling barrier is investigated using the Bardeen transfer Hamiltonian. The tunneling current oscillates with an increasing magnetic field for a fixed bias. Many peaks are observed with an increasing external bias under a fixed magnetic field. Spin polarization of the tunneling current is tuned by changing the external bias under a weak magnetic field.

Figure 1

Potential profile of the tunneling structure. The quantum dot is embedded in the barrier.

Figure 2

The Landau-level fan in (a) DMS and (b) NMS 2DEG for spin-up (the thin solid lines) and spin-down (the thin dashed lines) electron. The thinner lines correspond to the energies of the spin-up (solid lines) and the spin-down (dashed lines) electron states in the QD. The thickest curves depict the Fermi energy versus the magnetic fields, where the solid line and the dashed-dotted line correspond to the electron density ${\aleph }_e=4\times {10}^{11}∕{\mathrm{cm}}^2$ and $2\times {10}^{11}∕{\mathrm{cm}}^2$, respectively. We set $T=1\mathrm{K}$, $\hslash {\omega }_0=15\mathrm{meV}$.

Figure 3

The tunneling current versus the magnetic field for a fixed bias $(\Delta \mathrm{V}=10\mathrm{mV})$ for the (a) NMS∕DMS QD∕NMS and (b) DMS∕NMS QD∕DMS cases. The insets show the tunneling current for different spin orientations. Parts (c) and (d) show the corresponding energy spectra in the emitter and the QD. The thick solid lines denote the Fermi energy in the emitter, the thin solid and dashed lines for the spin-up and the spin-down Landau levels in the emitter and the thicker solid and dashed lines for the spin-up and the spin-down QD states. We set $\hslash {\omega }_d=15\mathrm{meV}$, $\Gamma =0.2\mathrm{meV}$, and $T=1\mathrm{K}$.

Figure 4

The tunneling current versus the external bias for two different magnetic field values and two different configuratons: NMS∕DMS QD∕NMS [(a) and (b)] and DMS∕NMS QD∕DMS [(c) and (d)]. The insets show the tunneling current for different spin orientations. The energy spectra are shown as a function of the external bias in (e) and (f), and the line types are the same as in Figs. 3c, 3d. We used $\hslash {\omega }_0=15\mathrm{meV}$, $\Gamma =0.2\mathrm{meV}$, $T=1\mathrm{K}$, and $\Delta E_0=E_0^d-E_0^e$, where $E_0^{d,e}$ are the quantized energies along the $z$ axis of the QD and the 2DEG.