Advanced Methods of Semiconductor Research Seminar – Tuesday 17th of June 2025
We cordially invite you to Advanced Methods of Semiconductor Research Seminar on Tuesday 17th of June 2025 at 13:15 in room 321, building A-1, where there will be delivered a lecture:
X-ray diffraction of nanowires – opportunities and challenges
by Dr. Aleksandra Wierzbicka
from Institute of Physics, Polish Academy of Sciences in Warsaw
Lecture abstract:
In general, nanowires (NWs) are almost strain-free objects without lattice misfit defects that could propagate into the crystalline structure, even if they are grown on highly lattice-mismatched substrates. Consequently, the growth of complicated heterostructures in the form of NW having crystallographic quality which is not available in similar planar structures is possible. However, to obtain high structural and optical quality of NWs, their growth procedure must be precisely controlled. X-ray diffraction (XRD) is one of the most important methods to evaluate properties of NW system. It allows efficient detection and visualization of the arrangement and orientation of the NWs, as well as imperfections of their crystal lattice. The method also allows to analyze NW distribution over large surface areas1.
In this talk, I will present the advantages of X-ray diffraction techniques to analyze GaN nanowire systems. I will show that, in contrast to planar layer measurements, diffraction on nanowire systems is different. In particular, it should be taken into account that the X-ray spectra obtained are influenced not only by the crystallographic quality of the nanowires but, above all, by their planar distribution, inclination, alignment in the plane of the structure under study, and the quality of the interface with the substrate.
I will present the results of XRD measurements of GaN nanowires grown using the plasma-assisted molecular beam epitaxy (PAMBE) technique. I will start by discussing the effect of the nitridation temperature of the Si substrate on the epitaxial alignment of GaN nanowires2. I will also demonstrate that the quality and crystallographic orientation of the GaN nanowires is also affected by the orientation of the substrate used3. I will also show how the use of additional buffer layers – amorphous (such as aluminum oxide)4 and crystalline (such as zirconium nitride)5 – between the substrate and the GaN nanowire affects the X-ray diffraction image. I will show that broad diffraction image is not necessarily associated with a deterioration of the crystallographic quality of the nanowires. For that, I will use the GIXRD technique that allows a completely different interpretation of the obtained image, being consistent with additional microscopic measurements.
[1] A.N. Danilewsky, et al. Phys. Status Solidi A, 2011, 208, 2499–2504.
[2] A. Wierzbicka, et al. Nanotechnology, 2013, 25, 035703.
[3] A. Wierzbicka, et al. Applied Surface Science, 2017, 425, 1014-1019.
[4] M. Sobanska, et al. Nanotechnology, 2020, 31, 184001.
[5] K. Olszewski, et al. Nanomaterials, 2023, 13, 2587.
