Fabrication and luminescence properties of self-assembled CdTe quantum dots embedded in an MnTe matrix

The growth of self-assembled CdTe quantum dots embedded in cubic MnTe by molecular beam epitaxy is reported. The dots are forced to form despite a small lattice mismatch of 2.3% between the dot and the barrier materials. Their properties are studied by means of time integrated and time resolved photoluminescence at various temperatures and magnetic fields. We demonstrate a considerable diffusion of Mn ions from the MnTe barrier into nominally nonmagnetic CdTe quantum dot, which is manifested as an enhancement of their magneto-optical effects, such as the Zeeman splitting of excitonic levels in the dots.

Figure 1

The 2D-3D growth mode transition typical for the formation of self-assembled QDs in the RHEED pattern: (a) 2D surface after the deposition of 6-ML CdTe on MnTe barrier and (b) the formation of 3D islands after coverage and thermal desorption of a tellurium layer.

Figure 2

PL spectrum at 10 K from the sample containing CdMnTe/MnTe QDs, solid line, and from a reference sample, containing $1\mu \text{m}$-thick MnTe layer, dashed line. Excitation at energy below the energy gap of MnTe, 442 nm (2.80 eV). The high energy line (HL) is attributed to the intra-${\text{Mn}}^{++}$ transition, the low energy line (LL) to the emission from the QDs. Both spectra are normalized, so that we can do the comparison between them.

Figure 3

Temperature dependence of the spectral position of HL and LL. Excitation line 442 nm (2.80 eV).

Figure 4

(a) A typical PL line attributed to the emission from an individual QD at an external magnetic field. The red shift and circular polarization of this line prove the presence of the giant Zeeman splitting within the dot. $T=2\text{K}$, magnetic field applied in Faraday geometry. (b) The spectral position of the PL line determined from a fit with a Gaussian vs magnetic field. Solid line—fit with a modified Brillouin function [Eq. (1)] with parameters [Eq. (2)] $E_{\text{S}}=41\text{meV}$ $T_{\text{eff}}=5.6\text{K}$. Inset: the decrease in the spectral width of this PL line with an increasing magnetic field.

Figure 5

(a) Energy shifts at saturation, $E_{\text{S}}$, (b) effective temperature, $T_{\text{eff}}$ of 18 PL lines from individual QDs vs their spectral position at 0 T determined from the fits with the Brillouin function.