Our scientists have discovered that a coverage of GaN nanowires with an ultrathin oxide shells significantly increases intensity of GaN luminescence and prevents photodegradation of the nanowires exposed to an environment. That finding is important for future application of nanowires in semiconductor light emitters, as LEDs or lasers.

Semiconductor nanostructures, particularly nanowires, are promising building blocks for next-generation electronic devices. Due to their small diameter (~100 nm) and limited contact area with the substrate, the stresses that form at the nanowire/substrate interface are efficiently relaxed along the sidewalls of the nanowires, preventing the generation of defects. This structure enables the production of materials with exceptionally high crystalline quality, even on substrates with completely different crystal structures, or even on amorphous substrates, in contrast to the planar structures commonly used today. Furthermore, the high surface-to-volume ratio of nanowires makes them ideal candidates for applications in chemical and biological sensors.

However, in some applications, such as light emitters, the strong influence of ambient conditions on the physical properties of nanowires is undesirable. As a result, significant efforts are being made to passivate surface states, often by coating the nanowires with protective shells.

In our recent work published in Small (Vol. 20, No. 44, 2024), in collaboration with researchers from Wroclaw University of Science and Technology and the University of Economics in Katowice, we demonstrated that the deposition of AlO_x or HfO_x shells significantly enhances the luminescence of GaN nanowires. However, our X-ray diffraction and Raman spectroscopy measurements reveal that the shells induce deformation in the nanowire crystal lattice. Consequently, a balance must be struck between the various mechanisms introduced by these shells to achieve highly efficient systems for UV optoelectronics. Specifically, we showed that the optimal design involves reducing the shell thickness to a single atomic layers, even if the thickness is nonuniform, as observed via electron microscopy. This approach allows for luminescence enhancement and photodegradation prevention while minimizing lattice deformation in the GaN core

Importance of these results has been underlined by the editors who have chosen the article’s graphics as the cover picture of the Small journal.