High-quality epitaxial thin films are key components of almost all modern electronic devices. During epitaxial thin film growth, lattice mismatch between the substrate and the film generates elastic strain, which eventually leads to defects that relieve the strain beyond certain thicknesses of film growth. These defects can deleteriously affect the electronic properties of the thin film such as its electron mobility. To solve this problem, scientists considered the asymmetric crystallographic tilt as a promising growth pattern, but first needed to characterize the detailed structure and strain relaxation mechanisms at heteroepitaxial interfaces.
A group of researchers used in situ synchrotron-based X-ray diffraction techniques to reveal how the crystallographic orientation and the grain size of a growing epitaxial film change during the electrochemical deposition. In the Journal of Applied Physics, they present the first real-time observation of asymmetric tilt boundary dynamic responses at the film-substrate interface of a film during growth.
The bismuth films on gallium arsenide investigated in this work make attractive candidates for spintronic devices. Their properties and applications are closely related to the epitaxial structure of bismuth on gallium arsenide. Combining high-energy X-rays and a large area detector, the researchers simultaneously monitored several Bragg reflections during thin film electrodeposition under various deposition conditions. They found that a single crystallographic orientation of the bismuth film could be selected by controlling the electrodeposition conditions. They also noted that the bismuth film formed an asymmetric tilt to relieve the structural mismatch.
After a threshold thickness, the tilt gradually relaxed. Understanding and controlling this strain relaxation process has important implications for the production of high-quality, strain-free epitaxial films central to modern electronic devices.
Source: “Relaxation of asymmetric crystallographic tilt: In situ x-ray diffraction studies of epitaxial electrodeposition of bismuth on GaAs (110),” by Xin Huang, Manuel Plaza, J. Y. Peter Ko, Héctor D. Abruña, and Joel D. Brock, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5026630.
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