Properties of ZnO layers deposited by ''photo-assisted'' spray pyrolysis

Layers of ZnO have been deposited onto glass substrates by ''photo-assisted'' spray pyrolysis using zinc chloride and zinc acetate as precursors in aqueous and non-aqueous solutions. The structure of these films has been shown by reflection high energy electron diffraction (RHEED) to be hexagonal, the crystallites exhibiting a pronounced preferred orientation with their (0002) planes lying parallel to the substrate. The transmission properties of layers deposited using an aqueous solution of zinc acetate were found to be superior. In their as-deposited form the films repeatedly exhibited carrier concentration, Hall mobility and resistivity values of similar to (1-2) X 10(17) cm(-3), similar to 0.1-0.2 cm(2) V-1 s(-1) and similar to 150-600 Ohm . cm respectively. However, following annealing at 400 degrees C for 15 min in forming gas (H-2 + N-2), these parameters improved to similar to 5 X 10(19) cm(-3), similar to 29 cm(2) V-1 s(-1) and similar to 1.5 X 10(-2) Ohm . cm respectively. Annealing did not change the transmittance but there was a noticeable improvement in the degree of preferred orientation. The considerable improvement in the electrical properties after annealing can be largely attributed to the increases in carrier concentration and mobility due to the change in stoichiometry and possibly a reduction in inter-granular potential barriers respectively.