Raman and cathodoluminescence analysis of transition metal ion implanted Ga2O3 nanowires

The structural and luminescence properties of gallium oxide nanowires doped with chromium or manganese have been investigated. Undoped Ga2O3 nanostructures have been fabricated by a thermal evaporation method, while doping was subsequently achieved by ion implantation followed by thermal annealing. Scanning electron microscopy (SEM) analysis has shown that this doping process does not alter the morphology of the nanostructures. Ion implantation results in partial amorphization of the crystal lattice, as deduced from Raman spectroscopy studies. Thermal annealing at different temperatures was carried out in order to restore the crystallinity of the nanowires. Raman spectroscopy analysis demonstrates that recrystallization starts at about 700 °C and a complete recrystallization is achieved at about 1000 °C. Cathodoluminescence (CL) analysis has been used to study the emissions in the 300-900 nm range. As-implanted nanowires virtually do not emit any light, which is related to their poor crystal quality and the implantation induced defects. Thermal annealing results in effective CL emission. In particular, a clear correlation between crystallinity of the nanowires doped with Cr and the emission from the 2E-4A2 and 4T2-4A2 intraionic transitions has been observed. On the other hand, emissions directly related to intraionic transitions of Mn have not been found in the nanowires implanted with this ion. The influence of the implantation process and annealing temperature on the observed changes in the donor-acceptor pairs (DAP) band of Ga2O3 is discussed.