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

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 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.