# Influence of Contacts and Applied Voltage on a Structure of a Single GaN Nanowire
## 5 Summary and Outlook  
In our study, a strong influence of the different types of metallic contacts on the strain state of GaN NWs with diameters of 200 nm and 350 nm was demonstrated using coherent X-ray diffraction of the 10\(\bar{1}\)0 GaN Bragg peak. Employing the developed FEM model, the maximum tensile strength in the nanowires was calculated for the different bending states induced due to the deposited Au contacts. For the NWs with 350 nm in diameter, the maximum tensile strength raised to \(2\times 10^{8}\) Pa after the contacts deposition. Further, the influence of the applied voltage bias on the strain field evolution until the breakdown of the nanostructures was investigated. The strain in the GaN NWs increased up to the ultimate tensile strength of \(6\times 10^{8}\) Pa corresponding to two volts of applied bias, at which the nanowire was broken. This ultimate tensile strength was in a good agreement with out previous work, while the breakdown voltage deviation was explained by the different geometry of the contacts and their possibly different breakdown behavior. In the case of the NWs with the diameter of 200 nm, it was demonstrated that they bend already by the interaction with the substrate. The applied Au contacts disturbed the scattered X-ray intensity distribution of the Bragg peak even more. Additionally, the contacts fixation of this type of NWs was less stable, which made their investigation with the current diameter to length ratio rather challenging. For our future experiments, the length of the NWs with diameters below 350 nm is planned to be shorter than 2 \(\upmu\)m.  
An additional type of fixation with the NWs positioned on the top of the Au contacts demonstrated for the GaN NWs with the diameter of 200 nm a much weaker \"contact-nanostructure\" fixation. The GaN NW was disconnected already after the first applied voltage bias of 0.5 volts. Due to these reasons, the operando study of the nanowires with this type contacts was not successful. We expect that the results of our work will contribute to the development and manufacture of the devices based on the nanostructures and may help the high-technology industry development. The following are available online at [[https://www.mdpi.com/article/10.3390/app11209419/s1](https://www.mdpi.com/article/10.3390/app11209419/s1)]([https://www.mdpi.com/article/10.3390/app11209419/s1](https://www.mdpi.com/article/10.3390/app11209419/s1)), Section S1: Free-lying NWs; Section S2: SEM images of the contacted NWs before and after the experiment; Section S3: Evolution of the scattered intensity of the NWs as a function of applied voltage; Section S4: Measurements of the GaN NWs with the Pt contacts. Figure S1: (a-c) The intensity distribution around 10\(\bar{1}\)0 GaN Bragg reflection of three different free-lying GaN NWs with diameters of 350 nm. (d-f) The same Bragg peaks from a different view perpendicular to the [0001] crystallographic direction. The figures demonstrate absence of the \"double-star\" structure,which was observed in the case of bent GaN NWs. Figure S2: (a,b) The intensity distribution around 1010 GaN Bragg peak of two free-lying GaN NWs with diameters of 200 nm. (c,d) A different view of these Bragg peaks from a direction perpendicular to the [0001] crystallographic axis. The Bragg peaks demonstrate the \"double-star\" structure typical for the bent GaN NWs. Figure S3: SEM images of the contacted GaN NWs. The first 350 nm GaN NW before (a) and after (b) applied voltage bias. The second 350 nm GaN NW before (c) and after (b) the maximum applied voltage. The 200 nm GaN NW before (e) and after (f) the applied voltage bias. Figure S4: SEM images of the second type of Au contacts. The NW with the diameter of 200 nm contacted on the top of the Au electrodes by melting procedure before (a) and after (b) applied 0.1 V of bias. (c) The 350 nm GaN NW on the top of Au contacts. Figure S5: Evolution of the intensity distribution around 1010 GaN Bragg reflection of the second contacted GaN NW with the diameter of 350 nm.