Impact of Native Point Defects on Elastic Properties of GaN Nanowires.

Native point defects can significantly affect the optical and electrical properties of GaN nanowires. However, how they change the mechanical performance remains unclear. Here, elastic properties of c-axis GaN nanowires with different native point defects concentrations have been quantitatively studied. GaN nanowires with a higher point defects density demonstrate lower Young's modulus and fracture strength as well as noticeable time-dependent anelastic behavior under the stress gradient. Whereas, the "cleaner" nanowires are much stronger and remain elastic without detectable hysteresis. Photoluminescence spectroscopy analysis indicates that the dominant point defects in the unintentionally doped GaN nanowires are Ga vacancies and the complex with O atoms at N sites. The observed "smaller-is-stronger" size effect aligns with the size-dependent point defect density in both types of nanowires. This work may clarify the longstanding inconsistencies regarding the elastic properties of GaN nanowires and serve as an example of how mechanical behaviors can be tailored through defect engineering.