Bi doping stimulation on the visible-light absorption of In2O3 ceramics

Abstract Bandgap engineering in semiconductors is a long-term subject in many interests. Doping Bi modifies the wide-bandgap semiconductor In2O3 by generating an in-gap state. The reflectance spectra show that an optical transition occurs at 1.2 eV inside the bandgap of In2O3 as a substitution of Bi atoms, which is in good agreement with the previously reported density functional theory (DFT) calculation by Sabino et al., Phys. Rev. Mater. 3 (2019) 034605. The detailed analyses illustrate that the trivalent Bi dopant sites on the In-site in a limited concentration maintaining the chemical state of In and O. For the higher doping concentration, the secondary phase of Bi2O3 forms even though no chemical state variation of the host In2O3. However, the free electron concentration decreases rapidly with increasing Bi doping concentration while unchaining oxygen vacancies. These results confirm that the trivalent Bi induces an occupied band in the In2O3 electronic structure and In-vacancy as an acceptor, promising host materials for the p-type doping. Furthermore, the extended DFT calculation to the other pnictogen atoms confirms the similar in-gap states and lower In vacancy formation energy, suggesting the possibility toward p-type oxide semiconductors using pnictogen doped In2O3.