Abstract
The transparent-conducting performance is estimated through figure-of-merit (FOM) value. To improve poor FOM value of pure ZnO thin films, boron ($\!{{B}}$) as a donor impurity was doped into the films. Direct-current magnetron sputtering was used to prepare ${{B}}$-doped ZnO (BZO) thin films from sintered ZnO targets with variable ${{\rm{B}}_2}{{\rm{O}}_3}$ content changing from 0 to 2 wt. %. The x ray diffraction analysis confirmed the preferably $c$-axis-oriented structure of hexagonal wurtzite ZnO host. The results also showed variation in the film structure versus the ${{\rm{B}}_2}{{\rm{O}}_3}$ content through calculations of crystal size and residual stress. Depending on the ${{\rm{B}}_2}{{\rm{O}}_3}$ content, a competition of interstitial and substitutional ${{\rm{B}}^{3 +}}$ ions induced more stress or relaxation in lattice structure of the films. At 1% ${{\rm{B}}_2}{{\rm{O}}_3}$, the BZO thin film had the best crystalline characterization with the lowest stress and large crystal size. In consequence, the BZO 1% film obtained the lowest resistivity of ${2.7} \times {{1}}{{{0}}^{- 3}}\;\Omega {\rm{cm}}$, average transmittance of 82.1%, and the best FOM value of ${18.8} \times {{1}}{{{0}}^2}\;{\Omega ^{- 1}}\;{\rm{c}}{{\rm{m}}^{- 1}}$. The transparent-conducting performance of the ZnO thin films deposited by direct-current (DC) magnetron sputtering was significantly enhanced through ${{B}}$ doping. The good-performance BZO film at 1% ${{\rm{B}}_2}{{\rm{O}}_3}$ is believed to be of use as electrodes in thin-film solar cells.
© 2020 Optical Society of America
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