The electron microscopy laboratory is working on optimizing the technology of growing GaN nanowires

Scientists from the Institute of Physics and Applied Mathematics of MIET traced the evolution of the GaN nanowires (NWs) shape obtained by plasma-activated molecular beam epitaxy and representing an array of vertical columns on a silicon substrate. Due to the high perfection of the crystal structure and large specific surface area, GaN NWs can be used in high-efficiency LEDs, sensors for volatile compounds, photodegradation of water, reduction of CO2 emissions into the atmosphere, etc.

Experimental samples of GaN NWs were obtained at The Paul-Drude-Institut für Festkörperelektronik (Germany), and their study was performed on an electron-ion microscope Helios NanoLab650, a transmission electron microscope Titan Themis 200 at MIET and using small-angle X-ray scattering at the European Synchrotron (ESRF).

MIET employees prepared cross sections of NWs at different distances from the substrate using the focused ion beam method. Electron microscopy made it possible to establish that they originally had a hexagonal cut. After the closure of adjacent NWs, the resulting concave sections are coalesced and the hexagonal shape of the NWs is restored. An analysis of their electron microscopic images with atomic resolution showed that, during growth, GaN decomposes in the region of edges, evaporation of nitrogen atoms, and the formation of a thin film of gallium atoms on the NWs facets. As a result of the described process, they acquire a roundish shape.

The results obtained deepen the understanding of the mechanism of formation of GaN NWs and are important for optimizing the technology of their growth. The results of the study were published in “Nanoscale Advances” journal in the article “Cross-sectional shape evolution of GaN nanowires during molecular beam epitaxy growth on Si (111)”, 2022, (DOI: 10.1039/D1NA00773D).