Microluminescence from ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ magnetic quantum dots containing only a few Mn ions

Self-assembled magnetic ${\mathrm{Cd}}_x{\mathrm{Mn}}_{1-x}\mathrm{Te}$ quantum dots (QDs) embedded in nonmagnetic ${\mathrm{Zn}}_{0.6}{\mathrm{Cd}}_{0.4}\mathrm{Te}$ were grown by molecular beam epitaxy. We achieved a large degree of dilution of Mn ions inside the QDs, $x_{\mathrm{Mn}}=0.003$, which allowed us to study single QDs containing only few Mn ions. The insight into properties of these structures was obtained by performing measurements of photoluminescence in an external magnetic field with a high spatial resolution by using immersion reflection objective. Approximate number of Mn ions inside dots and the size of the dots were found by comparison of the magnetic field evolution of the corresponding photoluminescence lines with calculations in terms of a muffin tin model developed originally to describe bound magnetic polarons.

Figure 1

(a) Microphotoluminescence spectra of $\mathrm{Cd}\mathrm{Mn}\mathrm{Te}∕{\mathrm{Zn}}_{0.6}{\mathrm{Cd}}_{0.4}\mathrm{Te}$ QDs with small amount of Mn taken in magnetic fields ranging from $-6\mathrm{T}\text{to}6\mathrm{T}$ (nonresonant excitation with $364\mathrm{nm}$ argon line), (b) the degree of polarization of photoluminescence from the whole QDs ensemble as a function of the magnetic field at $2\mathrm{K}$.

Figure 2

(a) Magnetic field dependence of an individual diluted magnetic QD from the low energy part of the spectrum (large dot), $T=2\mathrm{K}$. (b) Calculations of the shapes of PL lines in terms of the muffin tin model: $N_{\mathrm{cat}}=6600$; $N_{\mathrm{Mn}}=25$; $T_{\mathrm{eff}}=4.9\mathrm{K}$. (c) Magnetic field dependence of the position of the PL line: experimental points and theoretical calculations in terms of the muffin tin model for QDs with $x=0.0038$, $T=4.9\mathrm{K}$ and different sizes (lines). The bold line marks the best fit for $N_{\mathrm{Mn}}=25$. The error bars show the spectral widths of the PL lines determined from Gaussian fits. (d) Magnetic field dependence of the spectral width: experiment points and theoretical calculations (lines). The error bars of experimental points show the uncertainties of determination of the spectral width from the Gaussian fit.

Figure 3

(a) Magnetic field dependence of an individual diluted magnetic QD from the central part of the spectrum (medium dot), $T=2\mathrm{K}$. (b) Calculations of the shapes of PL lines in terms of the muffin tin model: $N_{\mathrm{cat}}=3600$; $N_{\mathrm{Mn}}=13$; $T_{\mathrm{eff}}=4.9\mathrm{K}$. (c) Magnetic field dependence of the position of the PL line: experimental points and theoretical calculations in terms of the muffin tin model for QDs with $x=0.0036$, $T=4.9\mathrm{K}$ and different sizes (lines). The bold line marks the best fit for $N_{\mathrm{Mn}}=13$. The error bars show the spectral widths of the PL lines determined from Gaussian fits. (d) Magnetic field dependence of the spectral width: experiment points and theoretical calculations (lines). The error bars of experimental points show the uncertainties of determination of the spectral width from the Gaussian fit.

Figure 4

(a) Magnetic field dependence of an individual diluted magnetic QD from the high energy part of the spectrum (small dot), $T=2\mathrm{K}$. (b) Calculations of the shapes of PL lines in terms of the muffin tin model: $N_{\mathrm{cat}}=1500$; $N_{\mathrm{Mn}}=5$; $T_{\mathrm{eff}}=4.9\mathrm{K}$.