The structure of threading defects in GaN nanorods

The proposal is to use the SuperStem facility at Daresbury to analyse the atomic structure of new threading defects observed in GaN nanorods grown by molecular beam epitaxy as part of a recent EPSRC grant, EP/D080762/1, joint between Bristol, Nottingham and Bath Universities. A model for these defects, which are planar faults, has already been derived as a result of low resolution observations in the transmission electron microscope in Bristol, and this has been used to propose a new nanorod growth mechanism. The SuperStem will enable us to directly analyse the displacements associated with these faults, and thereby clarify the growth model.

There is widespread interest in GaN and other semiconductor nanorod structures for new types of electronic device, but this is based to a large extent on the premise that nanorods are free of threading defects. Our research shows that this is not the case, but the nature and role of the defects remains in doubt. This project will clarify the nature of the defects and the role that they play in nanorod growth, and thereby help us to understand how they may be controlled and eliminated. This is central to the development of devices based on semiconductor nanorods.