Role of hydrogen in the n-type oxide semiconductor MgIn₂O₄: Experimental observation of electrical conductivity and first-principles insight

Hydrogen impurities significantly influence the electrical conductivity of oxide semiconductors like MgIn₂O₄, widely used in devices such as thin-film transistors. However, their role and chemical environment have not been fully clarified. This study investigated the conductivity of MgIn₂O₄ at elevated temperatures under air and H₂ atmospheres, revealing higher and reversible conductivity in H₂ due to hydrogen dissolution. Hall measurements, thermal desorption spectrometry, and nuclear magnetic resonance spectroscopy revealed that hydrogen dissolves in MgIn₂O₄, ionizing to produce electrons and interstitial protons. Density functional theory calculations indicate that hydrogen stabilizes near vacant octahedral cation sites, forming O-H bonds and shallow donor levels. Indium atoms at magnesium sites lead to shallow donor levels, whereas oxygen vacancies form deep levels. The results identify interstitial hydrogen and indium atoms at magnesium sites, rather than oxygen vacancies, as key donors under H₂-rich or low oxygen conditions, providing insights for controlling the conductivity of MgIn₂O₄ in devices.