Computational model of heterostructural TaC/AlGaN Schottky diodes

High Al-content Al_xGa_1–x N (AlGaN) alloys are promising ultra-wide bandgap materials for next-generation power electronics, but the lack of lattice-matched substrates remains a major bottleneck. Heterostructural rocksalt-wurtzite TaC(111)/AlGaN(0001) interfaces offer a potential route for lattice-matching around x=0.5. However, the atomic structure at interfaces between materials with different crystal structures can be more complex than at isostructural interfaces. To predict the stable TaC/AlGaN interface structures, we perform high-throughput density functional theory (DFT) calculations using an algorithm for systematic sampling of the possible stacking sequences of the atomic layers on the in-plane hexagonal lattice, for all combinations of (Ta, C) substrate termination, (Al/Ga, N) film nucleation, and (Al/Ga, N) wurtzite polarity. We then construct a phase diagram showing the interface structures with minimal free energy under variation of synthesis conditions. For the most relevant cases, we calculate the TaC/Al_0.5Ga_0.5N interface electronic structure with GW corrections of the DFT band energies and obtain band alignment and interface charges. Incorporating these results into device simulations, we demonstrate a practical design for a strain-free, high-efficiency TaC/AlGaN Schottky diode with low barrier height and vanishing interface charge.

[1] S. Mahatara and S. Lany, Phys. Rev. Appl. 22, 054044 (2024), https://doi.org/10.1103/PhysRevApplied.22.054044