X-ray absorption spectra of In(x)Ga(1-x)N alloys with insight from atom-specific simulations

We report N-K-edge x-ray absorption near-edge spectra of a set of In(x)Ga(1-x)N alloy epilayers with 0.36 < x < 0.87, including linear dichroism effects. Careful experimental and data treatment procedures lead to consistent variations of spectral features with In concentration and sample orientation with respect to the direction of linear polarization of the x-ray beam. Insight into the origin of spectral features is provided by a combination of ab initio simulations of the equilibrium structure and atom-by-atom spectral simulations. The relation between the spectral lineshape and the variations in the composition of the first coordination shell and the corresponding local structural distortions is discussed

Identification of four-hydrogen complexes in In-rich InxGa1-xN (x > 0.4) alloys using photoluminescence, x-ray absorption, and density functional theory

Postgrowth hydrogen incorporation in In-rich InxGa1-xN (x > 0.4) alloys strongly modifies the optical and structural properties of the material: A large blueshift of the emission and absorption energies is accompanied by a remarkable broadening of the interatomic-distance distribution, as probed by synchrotron radiation techniques. Both effects vanish at a finite In-concentration value (x similar to 0.5). Synergic x-ray absorption measurements and first-principle calculations unveil two different defective species forming upon hydrogenation: one due to the high chemical reactivity of H, the other ascribed to mere lattice damage. In the former species, four H atoms bind to as many N atoms, all nearest-neighbors of a same In atom. The stability of this peculiar complex, which is predicted to behave as a donor, stems from atomic displacements cooperating to reduce local strain

Identification of four-hydrogen complexes in In-rich InxGa1-xN (x>0.4) alloys using photoluminescence, x-ray absorption, and density functional theory

Post-growth hydrogen incorporation in In-rich InxGa1-xN (x>0.4) alloys strongly modifies the optical and structural properties of the material: A large blue-shift of the emission and absorption energies is accompanied by a remarkable broadening of the interatomic distance distribution, as probed by synchrotron radiation techniques. Both effects vanish at a finite In-concentration value (x0.5). Synergic x-ray absorption measurements and first-principle calculations unveil two different defective species forming upon hydrogenation, one due to the high chemical-reactivity of H, the other ascribed to mere lattice damage. In the former species, four H atoms bind to as many N atoms, all nearest neighbors of a same In atom. The stability of this peculiar complex, which is predicted to behave as a donor, stems from atomic displacements cooperating to reduce local strain