First-principles Calculation of L_3 X-ray Absorption Near Edge Structures (XANES) and Electron Energy Loss Near Edge Structures (ELNES) of GaN and InN Polymorphs

摘要

First principles calculations of LI XANES/ELNES of GaN and InN with both wurtzite and zinc-blende structures have been made using OLCAO (orthogonalized linear combinations of atomic orbitals) method. Super-cells with more than 100 atoms were employed. A core-hole was rigorously included in the calculation, and the photo absorption cross section (PACS) between the initial and final states was computed. Quantitative reproduction of experimental spectrum that is available in literature can be found when the PACS was computed. Although spectral shapes of two phases look similar, characteristic differences are predicted to appear at the first peak of the L_3 XANES/ELNES. The first peak is notably broader in the zinc-blende phases. The origin of the broadness is analyzed using partial density of unoccupied states (PDOS) and Mulliken charge. We then conclude that the broadness can be related to greater covalency of the zinc-blende phase as compared to the wurtzite phase.