Achieving p-type conductivity in ultrawide-bandgap oxides by overcoming hole polarons

A major shortcoming of ultrawide-bandgap (UWBG) semiconductors is their lack of bipolar doping. For UWBG oxides, n-type conductivity is often achievable, but p-type conductivity is usually inhibited by a tendency to form self-trapped holes (small polarons) [1]. This problem especially afflicts Ga₂O₃, which is among the most promising UWBG oxides, but in which polaronic hole trapping causes acceptors to have ionization energies exceeding 1 eV. Related materials, such as LiGaO₂, also suffer from hole trapping, preventing acceptor dopants from giving rise to p-type conductivity.

Recently, LiGa₅O₈ was claimed to be a p-type dopable, based on measurements of undoped material. Here, the electronic properties of potential acceptor dopant impurities in LiGa₅O₈ are calculated using hybrid density functional theory. As with the related compound LiGaO₂⁠, the heavy oxygen-derived valence bands lead to stable self-trapped holes in LiGa₅O₈⁠. Acceptor defects and dopants also bind trapped holes (or small polarons), which lead to large acceptor ionization energies [2]. Optical transitions associated with these defects are also calculated, in order to allow for possible experimental verification of their behavior.

References

[1] J. L. Lyons, D. Wickramaratne, and A. Janotti, Curr. Opin. Solid State Mater. Sci. 30, 101148 (2024).

[2] J. L. Lyons, JAP 135, 165705 (2024).