Experimental Analysis of Possible Origin of p-type Conductivity in Ultrawide Bandgap LiGa₅O₈Thin Films

Recently, we have discovered a new p-type ultrawide bandgap semiconductor based on LiGa₅O₈ with an energy bandgap of ~5.4 eV. The mist-CVD grown LiGa₅O₈ films show robust p-type conductivity at room temperature, representing the widest energy bandgap p-type oxide semiconductor. It is promising to integrate p-LiGa₅O₈ with n-type β-Ga₂O₃ to form pn junctions – addressing the key challenge in Ga₂O₃: lack of p-type. However, the origin of the p-type conductivity in LiGa₅O₈ remains unclear, with no theoretical explanation of the p-type conductivity so far. In this work, the influence of film compositions and post-deposition annealing on the p-type conductivity was systematically investigated. The results revealed that oxygen vacancies may play an important role in achieving p-type conductivity, as films with lower oxygen content exhibit higher hole concentration. The impact of different annealing atmospheres was also explored, finding that argon annealing enhances hole conductivity without altering film composition, while oxygen annealing reduces conductivity. Additionally, the uniformity of Li distribution in the films was confirmed from SIMS characterization. These insights provide a better understanding of the properties of LiGa₅O₈, paving the way for its integration into advanced power electronic devices.