Transparent bipolar semiconductors (TBSCs) are in demand for transparent electronics to serve as the basis for next generation optoelectronic devices. However, the poor carrier controllability in wide-bandgap materials makes the realization of a bipolar nature difficult. Only two materials, CuInO₂ and SnO, have been reported as TBSCs. To satisfy demand for the coexistence of transparency and bipolarity, we propose a design concept with three strategies; choice of early transition metals (eTM) such as Y³⁺ and Zr⁴⁺ for improving controllability of carrier doping, design of chemical bonds to obtain an appropriate band structure for bipolar doping, and use of a forbidden band-edge transition to retain transparency. This approach is verified through a practical examination of a candidate material, tetragonal ZrOS, which is chosen by following the criteria [1]. ZrOS exhibits an excellent controllability of the electrical conductivity (10⁻⁷ -10⁻² S cm⁻¹), p- or n-type nature with ∼10⁻² S cm⁻¹ by Y or F doping, respectively, and optically wide gap (below 10⁻⁴ cm⁻¹ up to ∼2.5 eV). This concept provides a new kind of TBSC based on eTM ionic compounds. In this talk, we also show an interesting phenomenon of other eTM semiconductor: carrier polarity inversion via doping-induced polymorph change in LaSeF [2].

References

[1] T. Arai, S. Iimura, J. Kim, Y. Toda, S. Ueda, and H. Hosono, J. Am. Chem. Soc. 139, 17175-17180 (2017).

[2] T. Arai, S. Iimura, and H. Hosono, Chem. Matter. 30, 597-601 (2018).