We investigated electroluminescence (EL), photoluminescence (PL) and micro-photoluminescence (μ-PL) of self assembled CdTe quantum dots (QDs) embedded in different II-VI materials: ZnCdTe, ZnMgTe and CdMgTe. Our structures were grown by Molecular Beam Epitaxy (MBE) employing a new self formation method of the QDs proposed recently by Tinjod et al. [1]. The most important advantage of this method is the possibility of quantum dots formation even when the lattice mismatch between the dot and the barrier material is as small as 2.8%. Another advantage is the possibility of in-situ observation of the 2D-3D transition by RHEED (Reflection of High Energy Electron Diffraction).
The surface of our structures was examined by Atomic Force Microscopy. From these measurements, we obtained the density of dots of the order of 10¹⁰ cm^-2, the average in-plane diameter and the average height being about 30nm and 7nm, respectively.
For EL measurements we have introduced CdTe quantum dots layer into a p-n junction. We have chosen carefully the n-type and p-type materials taking into account their electrical and optical properties. The quality of p-n junctions was characterized by current-voltage measurements. We have studied temperature and voltage dependencies of the luminescence.
The typical PL and EL spectra of a quantum dots layer consist of a very broad line. Its spectral width is determined by inhomogeneity of the sizes and chemical compositions of the quantum dots in the ensemble. In the case of μ-PL, we decrease the diameter of the excitation spot down to 2 μm. The PL line splits into a large number of sharp spikes with the spectral width in range of 100 μeV. The narrow lines are attributed to individual quantum dots. We found that we can significantly shift the position of the luminescence line, when we change the composition of the barrier, from 1.7eV to 2.3eV.
[1] Tinjod F., Gilles B., Moehl S., Kheng K., Mariette H. Appl.Phys.Let.,v 82, 24, p.4340
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