Deposition of p-type NiO films by chemical spray pyrolysis

Abstract

NiO films were fabricated by spray pyrolysis method using aqueous and alcohol based solutions of Ni chloride and acetate, and growth temperatures in the range of 350–500 °C. Films are of cubic NiO phase, the crystallite size increases and film thickness decreases with the film growth temperature. When NiO films are prepared from chloride solutions the crystallites grow along the (111) plane parallel to the substrate while, by contrast, they grow with no preferred orientation when grown from nickel acetate solutions. Spray of NiCl2 results in films with uneven thickness, rough surface and porous microstructure while smooth films with uniform thickness can be obtained spraying Ni acetate solutions. Effect of Li-doping has been studied with NiO films from acetate solutions, LiCl and LiNO3 were used as dopant sources. According to XRD, sprayed NiO:Li films are of NiO phase where the lattice parameter decreases with increasing Li concentration in solution indicating the incorporation of Li atoms into NiO lattice. NiO and NiO:Li films show p-type conductivity, Li-doping decreases resistivity by two orders of magnitude, from ca. 300 to some Ω cm, as the carrier concentration increases from 1016 to 1018 cm−3 ([Li+] = 25 at.%, LiNO3). At similar doping rates LiNO3 is more efficient dopant source compared to LiCl.