Boron-doped ZnO films grown by successive chemical solution deposition

ZnO films are deposited on various substrates from zincate solutions (0.1 M) containing boron with a B/Zn atomic ratio of 5%. These films show an optimum n-type resistivity of 40-60 Omega cm. The composition, structure and morphology of the films are studied using x-ray photoelectron spectroscopy, x-ray diffraction (XRD) and scanning electron microscopy. The optical properties of the films are investigated by transmittance and photoluminescence (PL) spectroscopy. The XRD results reveal that the films consist of only hexagonal ZnO with no other crystalline trace compounds. Boron enters the film with almost the same ratio as added into the solution. Other impurities such as Cl and N can also enter the film from the bath solution. Films contain, most likely, zinc hydroxide but in the amorphous phase. The films' hexagonal lattice constants match those for un-doped films. The as-grown films have optical transmittance 80% (800 nm) and a direct band gap energy of 3.35 +/- 0.05 eV, which reduces to 3.24 +/- 0.04 eV upon thermal annealing. The room-temperature PL properties of the films prepared from different bath solutions are presented. The effect of thermal annealing and the bath composition on the UV and visible emissions are discussed.