Tight-binding branch-point energies and band offsets for cubic InN, GaN, AlN, and AlGaN alloys

Abstract

Starting with empirical tight-binding band structures, the branch-point (BP) energies and resulting valence band offsets (VBOs) for the zincblende phase of InN, GaN and AlN are calculated from their k-averaged midgap energy. Furthermore, the directional dependence of the BPs of GaN and AlN is discussed using the Green's function method of Tersoff. We then show how to obtain the BPs for binary semiconductor alloys within a band-diagonal representation of the coherent potential approximation (CPA) and apply this method to cubic AlGaN alloys. The resulting band offsets show good agreement to available experimental and theoretical data from the literature. Our results can be used to determine the band alignment in isovalent heterostructures involving pure cubic III-nitrides or AlGaN alloys for arbitrary concentrations.

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“…Valenceband offsets InAs v = 0.06 and AlAs v = −0.59 eV with respect to GaAs are obtained from the methods in Refs. [50,51]. The TB model consists of on-site terms (orbital energies) and coupling terms (overlap), which are chosen to best reproduce the binary bulk band structure.…”

Understanding band alignments in semiconductor heterostructures: Composition dependence and type-I–type-II transition of natural band offsets in nonpolar zinc-blendeAlxGa1−xN/AlyLandmann1, Rauls2, Schmidt3 2017Phys. Rev. B19060View full textAdd to dashboardCite

“…The determination of band discontinuities from ab initio calculations inevitably necessitates the alignment of energy levels of the respective interfacing semiconductor alloys to a common energy reference. Common choices of universal alignment levels are the vacuum level following Anderson's electron-affinity rule [30], characteristic marker levels in the electronic structure (e.g., core-level energies) [31][32][33][34][35], microscopic and macroscopic averages of the (electrostatic) onsite potentials [36][37][38], or charge neutrality levels [39][40][41], branchpoint energies, respectively [42][43][44]. Band offsets derived from alignment to a universal reference point as the vacuum level or branch-point energies, without making reference to particular strain conditions of the involved materials, are termed natural or unstrained.…”

“…Wei et al [63] used a combination of electron holography and cathodoluminescence measurements to determine the strained band offsets in a zb-GaN/Al 0.3 Ga 0.7 N heterostructure grown on 3C-SiC substrate yielding valence and conduction band offsets of −0.13 and 0.65 eV, respectively, and a high conduction-to-valence band-offset ratio of 5:1. A smaller zb-GaN/Al 0.3 Ga 0.7 N band-offset ratio of 0.5/0.15 ≈ 3.3 was determined by Mourad [44] using branch-point alignment of empirical tight-binding band energies to determine unstrained natural band offsets. These values are slightly different from the previously discussed band offsets between the wurtzite-type group-III nitride analogs [57,60].…”