Category Archives: Quantum dots

Numerical simulation of TEM images for In(Ga)As/GaAs quantum dots with various shapes

Quantum dots, ,

Semiconductor quantum dots (QDs) are of interest in many application areas due to their electronic properties. Transmission electron microscopy (TEM) images can be used to examine the QD geometry, distribution and strain profile, which will be helpful in the fabrication of QDs with specific electronic properties.

In order to link the contrasts in TEM images with shapes and concentration of these QDs it is crucial to combine strain calculations with TEM image simulations. In collaboration with researchers from TU Berlin, we recently presented a mathematical model and a tool chain for the numerical simulation of TEM images for semiconductor QDs, published in Optical and Quantum Electronics (Numerical simulation of TEM images for In(Ga)As/GaAs quantum dots with various shapes). We simulated lens-shaped and pyramidal indium gallium arsenide QDs embedded in a gallium arsenide matrix and compared the resulting TEM images to experimental ones. This tool chain will be applied to generate a database of simulated TEM images, which is a key element of a novel concept for model-based geometry reconstruction of semiconductor QDs, involving machine learning techniques.

This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy—MATH+ (Project EF3-1) and CRC 787 “Semiconductor Nanophotonics” under Project A4.

Electronic properties of In(As,Sb,P) graded–composition quantum dots

Quantum dots,

Graded-composition quantum dots grown using liquid-phase epitaxy techniques in the In(As,Sb,P) material system cover the mid-infrared spectrum (wavelengths of 3 to 5 μm), which is important for a wide range of applications, e.g. in gas sensing or energy
harvesting. The particular strength of the growth process from the liquid phase is that
composition gradients through a nanostructure can be intentionally achieved, facilitating the fine-tuning of the optoelectronic properties together with a significant improvement of the crystal quality. In collaboration with researchers from PDI and IKZ Berlin as well as Prof. Karen M. Gambaryan from Yerevan State University, Armenia, we have investigated
nucleation process and electronic properties of In(As,Sb,P) graded-composition quantum dots in a systematic study, published recently in ACS Applied Electronic Materials.

We have computed the electronic properties for different heights and diameters, as
observed in the ensemble and combined these results with the experimentally observed diameter distribution to simulate ensemble absorption spectra at room temperature. The simulated absorption peak wavelength (3.829 μm) is in excellent agreement with the
experimentally observed one (3.83 μm), facilitating the application of our simulation framework in theory-driven design of In(As,Sb,P) graded-composition quantum dots that fulfill the requirements of specific devices.

This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – The Berlin Mathematics Research Center MATH+ (Project AA2-5). Prof. Gambaryan’s visit to WIAS Berlin was funded by Deutscher Akademischer Austauschdienst (DAAD).

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