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 ~ 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.