Understanding band alignments in semiconductor heterostructures: Composition dependence and type-I–type-II transition of natural band offsets in nonpolar zinc-blendeAlxGa1−xN/Aly

Abstract

The composition dependence of the natural band alignment at nonpolar Al x Ga 1−x N/Al y Ga 1−y N heterojunctions is investigated via hybrid functional based density functional theory. Accurate band-gap data are provided using Heyd-Scuseria-Ernzerhof (HSE) type hybrid functionals with a composition dependent exact-exchange contribution. The unstrained band alignment between zincblende (zb) Al x Ga 1−x N semiconductor alloys is studied within the entire ternary composition range utilizing the Branch-point technique to align the energy levels related to the bulklike direct v → c and indirect, pseudodirect, respectively, v → X c type transitions in zb-Al x Ga 1−x N. While the zb-GaN/Al x Ga 1−x N band edges consistently show a type-I alignment, the relative position of fundamental band edges changes to a type-II alignment in the Al-rich composition ranges of zb-Al x Ga 1−x N/AlN and zb-Al x Ga 1−x N/Al y Ga 1−y N systems. The presence of a direct-indirect band-gap transition at x c = 0.63 in zb-Al x Ga 1−x N semiconductor alloys gives rise to a notably different composition dependence of band discontinuities in the direct and indirect energy-gap ranges. Below the critical direct-indirect Al/Gacrossover concentration, the band offsets show a close to linear dependence on the alloy composition. In contrast, notable bowing characteristics of all band discontinuities are observed above the critical crossover composition.

Layered Trichalcogenidophosphate: A New Catalyst Family for Water Splitting

“…Typically, the type I heterostructure has a symmetrical offset of potential barriers for the electrons and holes, where direct exciton transition occurs at the heterointerface. In type II heterostructures, the electrons and holes are localized on different sides of the heterointerface, which results in an indirect exciton transition [ 57 – 59 ]. The type II band alignment results in separation of the photo-generated electrons and holes, thus enhancing the photocatalytic efficiency.…”

Band Alignments of Ternary Wurtzite and Zincblende III-Nitrides Investigated by Hybrid Density Functional Theory

“…17 The variance in the reported band offset values is due to the choices of (i) approaches used to construct the band structures (such as the hybrid density functional theory, the k•p perturbation theory, and the tight-binding model) and (ii) energy references (such as the vacuum level, average electrostatic potentials, charge neutrality levels, and branch-point energies). 18 It is important to note that band alignments procured without the impact of strain are known as natural or unstrained band alignments, which are essential to determine the band alignments under a certain strain condition by incorporating deformation potentials. 19 In this work, a unified hybrid functional is introduced to determine band gaps and electron affinities of unstrained binary and ternary, wz-and zb-IIInitrides.…”

“…For instance, the reported valence band offsets of the unstrained zb-AlN/GaN interface range from 0.25 to 1.00 eV . The variance in the reported band offset values is due to the choices of (i) approaches used to construct the band structures (such as the hybrid density functional theory, the k · p perturbation theory, and the tight-binding model) and (ii) energy references (such as the vacuum level, average electrostatic potentials, charge neutrality levels, and branch-point energies) …”

Band offsets of Al x Ga1−x N alloys using first-principles calculations

“…A different approach which is more suitable for alloy systems is the alignment with respect to the branch point energy of each material [71,72]. The branch point energy or charge neutrality level of each material is given by [71]…”