Chemical Design and Example of Transparent Bipolar Semiconductors

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. 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.