Electronic Structure of Rock Salt Alloys of Rare Earth and Group III Nitrides

Abstract

Lattice parameters and electronic properties of RE1−xAxN alloys, where RE = Sc, Y, Lu and A = Al, Ga, and In, have been derived from first principles. The materials are expected to exhibit a linear decrease in cubic lattice parameters and a tendency to a linear increase in band gaps as a function of composition. These effects are connected with a strong mismatch between ionic radii of the RE and group III elements, which leads to chemical pressure in the mixed RE and group III nitrides. The electronic structures of such systems are complex, i.e., some contributions of the d- and p-type states, coming from RE and A ions, respectively, are present in their valence band regions. The findings discussed in this work may encourage further experimental efforts of band gap engineering in RE-based nitrides via doping with group III elements.

Electronic Structure of Ternary Alloys of Group III and Rare Earth Nitrides

“…Similar results were published in previous studies of structural parameters of group III nitrides [20][21][22]28]. As presented in Figure 1, the dependencies of a hexagonal lattice parameter a on RE content in the materials reflect generally bigger ionic radii of RE ions [31], which was also discussed in the previous LDA-based studies for similar rock-salt systems [25]. One may notice an almost negligible lattice mismatch in In 1−x Sc x N systems.…”

“…Namely, the valence regions of these materials are mainly formed by the N states and some minor contributions of the p and d states coming from group and RE ions, respectively. The characteristic electronic structure of nitrides near VBM is unaffected by the doping, which was also found for the materials in an opposite regime of compositions, i.e., the rock-salt alloys of Al/Ga/In-doped RE N systems [ 25 ]. The unoccupied d -electron contributions coming from RE ions are located above the CBM region (not shown).…”

“…However, this effect is less pronounced in In-based systems due to the fact that the band structures of these semiconductors are dominated by the relatively narrow of InN. It is worth recalling that an opposite phenomenon was predicted for the rock-salt RE N materials doped with In, i.e, the band gap of such systems increases with increasing In content, as a result of the relatively wide band gap of rock-salt InN [ 25 ].…”

“…Recent investigations of electronic structures of ternary alloys of rock-salt RE nitrides revealed very strong band gap bowings in such materials, which are related to RE ionic radii mismatch in particular systems [ 24 ]. The rock-salt alloys of RE and group III nitrides exhibit a linear increase in [ 25 ], which is also closely connected to the ionic radii of dopant ions despite an opposite relation of band gaps in wurtzite AlN, GaN, and In materials. This may be explained by the fact that valence and conduction band regions of the rock-salt alloys are dominated by the contributions coming from RE ions, whereas the contributions of group III ions are located well below and well above the valence band maximum (VBM) and conduction band minimum (CBM) of a material, respectively.…”