Influence of catalysts on the electronic properties of gallium nitride nanomaterials

The current advancement in tailoring the morphological states of GaN nanomaterials (GaN-NMs) is highly pursued. However, utilising different types of catalysts during the synthesis could alter the outcome of the electronic response of the GaN-NMs. Herein, we demonstrate the applicability of the element- and surface-sensitive X-ray absorption spectroscopy (XAS) as a tool to distinguish Ga L- and N K-edges features of GaN-NMs synthesised with Ge, Ni, and Ge/Ni catalysts. In particular, we resolved the implication of tuning indirectly the unoccupied 2p states of N atoms corresponding to access the orbital hybridisation mixing at low temperatures. We propose that the type of catalysts play a role in determining the $s{p}^3$/$s{p}^2$ ratio of N orbitals, as observed with a deconvolution of XAS spectra. Temperature-dependent XAS exemplified the $s{p}^2$ hold majority contribution for Ni- and Ge-catalysed GaN-NMs until reaching the inflexion point at 80 K. On the other hand, Ge/Ni catalysed GaN-NMs display a minute-increasing trend of $s{p}^3$ contribution. We propose that the structure–property correlation can be realised from the XRD and XAS shifts, thus a simplified model of interconversion orbital arrangement of hybrid electronic states is proposed. To investigate the applications for optoelectronic applications based on the different shapes of the nanomaterials, current–voltage measurement reveals that Ge/Ni-catalysed GaN-NMs shows the best photoelectric response as credited to their largest surface area. This work provides an understanding of tailoring the electronic properties of GaN-NMs by morphology control.