Effects of B₂O₃ doping on the crystalline structure and performance of DC-magnetron-sputtered, transparent ZnO thin...

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 B₂O₃ 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 B₂O₃ content through calculations of crystal size and residual stress. Depending on the B₂O₃ content, a competition of interstitial and substitutional B³⁺ ions induced more stress or relaxation in lattice structure of the films. At 1% B₂O₃, 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 2.7×10^-3Ωcm, average transmittance of 82.1%, and the best FOM value of 18.8×10²Ω^-1cm^-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% B₂O₃ is believed to be of use as electrodes in thin-film solar cells.