Defect Mediated and Diode Degradation in Wide Band-Gap AlGaN Electronics

Ultra-wide-bandgap III-Nitride semiconductors such as GaN and AlGaN alloys have the potential to enable highly compact power circuits that operate with higher efficiency, greater power density, and function under extreme environments. In this contribution we use parameter-free density function theory (DFT) to improve our understanding of p-AlGaN//p-GaN interfaces found in diodes. We improve on DFT computed optical properties using a self-consistent DFT-ACBN0 (Hubbard-U) approach and find for example that the DFT bandgap for AlGaN, ~2.8 eV, increases with DFT-ACBN0 to ~4.5 eV, in excellent agreement with experimental results. Our results show that ordered and disordered bulk-AlGaN are energetically near-degenerate. Surprisingly, we find that stoichiometric surfaces and interfaces derived from AlGaN and GaN are metallic, in contrast to the corresponding insulating bulk systems. The only exception is p-doped disordered AlGaN, with a small indirect band-gap of ~0.2 eV. These results suggest that disordered p-doped AlGaN is a promising materials template for obtaining a gapped material and improving diode functionality. The introduction of carbon spacers in AlGaN//GaN interfaces for restoring a finite bandgap is likely unsuccessful since the carbon modified interfaces are predicted to remain metallic. Instead, we find evidence that C-C edges can induce amorphization in the carbon spacer. In summary, our preliminary results suggest that AlGaN//GaN interfaces with and without carbon spacers tend to decrease diode performance through bandgap closure, a tendency that may be avoided by increasing the abundance of disordered AlGaN in diode devices. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.