P-Type Spin-Coated Sol–Gel Cr₂O₃ Layer by Postannealing in Vacuum

The hole carriers of spin-coated sol-gel Cr₂O₃ could be activated successfully by postannealing at a temperature of more than 500 °C in a vacuum without doping. The sheet hole concentration increased with the increase in the postannealing temperature and could reach 5 × 10¹⁴ cm^-2 at a postannealing temperature of 680 °C. However, activating the hole carriers for annealing Cr₂O₃ in N₂ ambient at a low pressure of 3 mTorr and a temperature of 560 °C or higher was difficult. The N₂-annealed Cr₂O₃ could regain the same electrical properties as vacuum-annealed Cr₂O₃ by annealing under vacuum again. A comparison of the deconvoluted XPS spectra of the postannealed Cr₂O₃ in a vacuum and in N₂ ambient showed that the amount of Cr²⁺, Cr⁴⁺, Cr⁵⁺, Cr⁶⁺, and O vacancies was strongly correlated with the hole carrier creation of Cr₂O₃.