Behavior of aluminum adsorption and incorporation at GaN(0001) surface: First-principles study

Abstract

First-principles calculations are performed to study the energetics and atomic structures of aluminum adsorption and incorporation at clean and Ga-bilayer GaN(0001) surfaces. We find the favorable adsorption site changes from T4 to T1 as Al coverage increased to 1 monolayer on the clean GaN(0001) surface, and a two-dimensional hexagonal structure of Al overlayer appears. It is interesting the Al atoms both prefer to concentrate in one deeper Ga layer of clean and Ga-bilayer GaN(0001) surface, respectively, while different structures could be achieved in above surfaces. For the case of clean GaN(0001) surface, corresponding to N-rich and moderately Ga-rich conditions, a highly regular superlattice structure composed of wurtzite GaN and AlN becomes favorable. For the case of Ga-bilayer GaN(0001) surface, corresponding to extremely Ga-rich conditions, the Ga bilayer is found to be sustained stable in Al incorporating process, leading to an incommensurate structure directly. Furthermore, our calculations provide an explanation for the spontaneous formation of ordered structure and incommensurate structure observed in growing AlGaN films. The calculated results are attractive for further development of growth techniques and excellent AlGaN/GaN heterostructure electronic devices. V

Energetics and magnetism of Co-doped GaN(0001) surfaces: A first-principles study

“…Our results show that Co atoms tend to concentrate in surface layer and do not show a migration to GaN bulk, which implies that Co prefer to site at the surface, instead of incorporating in the bulk. To summarize, the preferred site of Co-doped GaN(0001) surface keeps always on the outermost surface, which is completely different from our previous study on Al incorporation in GaN(0001) surface that Al atoms prefer to migrate into deeper regions 21 .…”

“…Then, to study the behavior of Co atoms in GaN(0001) surface under different growth conditions, the clean GaN(0001)-2 × 2 surface and the Ga-bilayer GaN(0001)- Å as listed in Table I of Ref. 21 . By testing the optimum for slab thickness, we find that the deepest cobalt atoms do not exhibit a significant spurious interaction with the bottom surface for four GaN bilayer system.…”

“…21 . By testing the optimum for slab thickness, we find that the deepest cobalt atoms do not exhibit a significant spurious interaction with the bottom surface for four GaN bilayer system.…”

“…Almost all relevant definitions were given in our previous study 21 . ∆n Co is the excess or deficit of Co atoms with respect to the reference.…”

Role of Ag-alloy in the thermal stability of Ag-based ohmic contact to GaN(0 0 0 1) surface

“…The Climbing Nudged-Elastic-Band (C-NEB) method [18] is applied for finding the energy barrier. We first optimize the structural parameters for bulk GaN in the wurtzite structure, obtaining a ¼ 3:216 Å , c ¼ 5:239 Å , and the internal parameter u ¼ 0:377, which agree well with the previous reports [19,20]. The optimized bulk lattice parameters are then used to build the slab for the GaN(0 0 0 1)-ð2 Â 2Þ surface with four GaN bilayers.…”