A convenient, aqueous-based synthesis of stable HgTe nanocrystals with widely size-tunable room temperature emission between wavelengths of 1.2 to 3.7 mum is demonstrated. By the choice of the thiols, applied as stabilizers, we optimized the growth dynamics, the luminescence quantum yields (up to 40%), and a ligand-exchange procedure, required to transfer the nanocrystals from water to nonpolar organic solvents. The latter is greatly improved and facilitated by the use of mercaptoethylamine as initial stabilizer. The possibility to tune the HgTe nanocrystal sizes from 3 to 12 nm and to control their surface functionalities (hydrophobic and hydrophilic) makes them very promising for the development of infrared optical devices, emitting in the wavelength region between the telecommunications and the molecular vibrations.

A concept for the fabrication of highly symmetric quantum dots that are coherently embedded in a single crystalline matrix is demonstrated. In this approach, the formation of the quantum dots is induced by a transformation of an epitaxial 2D quantum well into an array of isolated precipitates with dimensions of about 25 nm. The formation process is driven by the immiscibility of the constituent materials resulting from their different lattice structures. The investigated PbTe/CdTe heterosystem combines two different cubic lattices with almost identical lattice constants. Therefore, the precipitated quantum dots are almost strain free and near thermodynamic equilibrium they exhibit the shape of small-rhombo-cubo-octahedrons.The PbTe/CdTe quantum dots, grown on GaAs substrates, display intense room temperature luminescence at wavelength around 3.2 µm, which makes them auspicious for applications in mid-infrared photonic devices.

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Epitaxial quantum dots with symmetric and highly facetted shapes are fabricated by thermal annealing of two-dimensional (2D) PbTe epilayers embedded in a CdTe matrix. By varying the thickness of the initial 2D layers, the dot size can be effectively controlled between 5 and 25nm, and areal densities as high as 3×1011cm−2 can be achieved. The size control allows the tuning of the quantum dot luminescence over a wide spectral range between 2.2 and 3.7μm. As a result, ultrabroadband emission from a multilayered quantum dot stack is demonstrated, which is a precondition for the development of superluminescent diodes operating in the near infrared and midinfrared.

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