Speaker
Description
Currently, intensive research in group III nitrides is focussed on improving the performance of commercial devices. This includes their heterostructures and/or alloys with other group III elements. Amongst the latter are ternary semiconductors such as Al$_{x}$Ga$_{1-x}$N, which are expected to give rise to unexpected photonic and magnetic functionalities when doped with magnetic ion species. This has prompted our study of the lattice sites, valence states and annealing behaviour of Fe ions in virgin and Mn (1 at.%) doped Al$_{x}$Ga$_{1-x}$N using $^{57}$Fe emission Mössbauer spectroscopy (eMS). Radioactive $^{57}$Mn$^{+}$ (T$_{1/2}$ = 1.5 min.) ions were implanted with 50 keV energy at ISOLDE/CERN into Al$_{x}$Ga$_{1-x}$N films grown by metalorganic vapour phase epitaxy (MOVPE) on sapphire substrates. eMS measurements were performed in the temperature range of 100 - 800 K. The room temperature spectra for Al$_{0.2}$Ga$_{0.8}$N acquired at emission angles ($\theta$$_{E}$) of 60$^\circ$ and 0$^\circ$show the presence of magnetically-split sextets in the “wings”, similar to features observed in GaN and AlN[1] and attributed to Fe$^{3+}$ on Al/Ga sites showing slow paramagnetic relaxations[2]. The central part of the spectra is characterised by paramagnetic Fe$^{2+}$ on Al/Ga sites associated with nitrogen vacancies. However, with Mn doping, the contribution of Fe$^{3+}$ is considerably reduced or negligible. This is coupled with the corresponding emergence of a single line component with Mössbauer parameters typical of Fe$^{4+}$ on Al/Ga sites, which are acceptors in AlGaN, suggesting the possibility of p-type doping. Results will be discussed and compared with Si doping.
[1] H. Masenda, et al., Journal of Magnetism and Magnetic Materials, 401 (2016) 1130.
[2] H. P. Gunnlaugsson, et al., Applied Physics Letters, 97 (2010) 142501.
