Masterthesis - electron tomography
Due to the ongoing miniaturization of modern semiconductor devices towards low dimensionality and nanometric size, interfaces between different materials are becoming increasingly important for the functionality of these devices and their performance. This fact is all the more significant because interfaces are three-dimensional (3D) objects: They have a topographic character, often described by crystallographically defined extended terraces and steps, and a transition region perpendicular to the interface formed by atom interdiffusion. The detailed characterization of such interfaces is frequently performed by atomic-resolution (scanning) transmission electron microscopy (S-TEM) studies, with limited validity due to the projection property of the 2D images.
We have recently introduced the advanced method of electron tomography, which allows reconstructing 3D structure information of semiconductor interfaces and thereby independently determining both morphological roughness and chemical intermixing (E. Paysen et al., “Interface tomography of GaInAs/AlInAs quantum cascade laser active regions”, Semicond. Sci. Technol. 38, 055009 (2023)). For this purpose, a tilt series of STEM images of the object under investigation is created, which determine the 3D structure through computer-aided reconstruction algorithms. The spatial resolution of this 3D reconstruction is directly related to the transmitted material thickness, including the interface, and depends on the type of material, i.e., the interaction between electron and matter. In the case of crystalline materials with extended interfaces, this relationship has not yet been systematically investigated.
The master thesis should address experimental investigations on the 3D resolution of the interface tomography by examining the interplay between beam divergence (a geometric effect of the converged STEM probe) and beam broadening (an unavoidable broadening due to multiple elastic scattering). For these investigations, silicon-based interfaces with well-defined morphological characteristics are available as model system, which are prepared by focused ion beam technique into customized tomography needles with different thicknesses.
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Project-Contacts
M.Sc. Ekaterina Paysen (paysen@pdi-berlin.de)
Dr. Achim Trampert (trampert@pdi-berlin.de)
Academic Europe, the European career network for Academics, Researchers and Scientists
