Bipolar Semiconducting Properties in α-SnWO₄ Based on the Characteristic Defect Structure

Diodes, memories, logic circuits, and most other current information technologies rely on the combined use of p- and n-type semiconductors. Although oxide semiconductors have many technologically attractive functionalities, such as transparency and high dopability to enable their use as conducting films, they typically lack bipolar conductivity. In particular, the absence of p-type semiconducting properties owing to the innate electronic structures of oxides represents a bottleneck for the development of practical devices. Here, bipolar semiconducting properties are demonstrated in α-SnWO₄ within a 100 °C temperature window after appropriate thermal treatment. Comprehensive spectroscopic observations reveal that Sn⁴⁺ is present in p-type α-SnWO₄ in a notably greater quantity than in n-type. This result strongly suggests that the Sn⁴⁺ substitutional defects on the W⁶⁺ sites contribute to hole-carrier generation in α-SnWO₄. We also find that oxygen vacancies are initially formed in Sn-O-W bonds and migrate to W-O-W bonds with changes in semiconducting properties from p-type to n-type. These findings suggest useful strategies for exploring p-type oxide semiconductors and controlling their carrier type by utilizing the octahedral structure.