First-principles band alignment engineering in polar and nonpolar orientations for wurtzite AlN, GaN, and B$_x$Al$_{1-x}$N alloys

Abstract

Boron aluminum nitride (B$_x$Al$_{1-x}$N) is a promising material for next-generation electronic and optoelectronic devices due to its ultra-wide bandgap, high thermal stability, and compatibility with other III-nitride semiconductors. Despite its potential, the band alignments of B$_x$Al$_{1-x}$N remain largely unexplored, although this information is essential for device design. In this study, we compute the valence and conduction band alignments of nonpolar ($a$-plane) and polar ($c$-plane) B$_x$Al$_{1-x}$N, and compare them with those of AlN and GaN. Using density functional theory, many-body perturbation theory, $GW_0$ method, and a novel passivation scheme, we find that they have near-zero valence band alignments for low-$x$ B$_x$Al$_{1-x}$N/AlN, while higher compositions ($x > $0.333) exhibit type I or II band alignments. The band alignments also show a notable dependence on surface polarity and the tetrahedral distortion of the B$_x$Al$_{1-x}$N structures. Our computed offsets are in good agreement with available experimental data. Due to their low valence band alignments and higher conduction band alignments, the B$_x$Al$_{1-x}$N/AlN heterostructures could be well suited for high-electron-mobility transistors and ultraviolet light-emitting diodes. The band alignments of B$_x$Al$_{1-x}$N determined in this study provide essential design guidelines for integrating these ultra-wide bandgap alloys into advanced semiconductor technologies.

Figures (3)

• Figure 1: Slab structures in the $c$-plane (left) and $a$-plane (right) orientations for AlN, B$_{0.500}$Al$_{0.500}$N, and w-BN. The slab structures are fully passivated by pseudohydrogen (psH) atoms in the $c$-plane. The $a$-plane orientations are unpassivated. The dashed lines indicate the slab lattice with surface normals in the horizontal direction. Red, blue, green, and black spheres represent boron, aluminum, nitrogen, and psH atoms, respectively.
• Figure 2: Band alignments for GaN and B$_{x}$Al$_{1-x}$N, where $E_\mathrm{VBM}$ and $E_\mathrm{CBM}$ are represented by blue and red columns, respectively. The columns are shaded according to the average tetrahedrality in the bulk B$_{x}$Al$_{1-x}$N structure, which are shown by the colormap. Blue and red dashed horizontal lines show the AlN $E_\mathrm{VBM}$ and $E_\mathrm{CBM}$, respectively. The vertical dashed gray lines separate the GaN and B$_{x}$Al$_{1-x}$N results. a) Shows the $c$-plane N-surface slabs, b) the $c$-plane M-surface slabs, and c) the $a$-plane symmetric slabs. Error bars indicate standard deviations of the band alignments of the structures of the same composition.
• Figure 3: Natural band alignments for GaN and B$_{x}$Al$_{1-x}$N calculated using the SSE approach, where $E_\mathrm{VBM}$ and $E_\mathrm{CBM}$ are represented by blue and red columns respectively, shaded according to the average tetrahedrality in the structure. Blue and red dashed lines show the AlN $E_\mathrm{VBM}$ and $E_\mathrm{CBM}$ respectively. Dashed gray lines separate the GaN and B$_{x}$Al$_{1-x}$N results. The opacity of the columns is proportional to the average tetrahedrality of the corresponding bulk structure.