Preparation Of ZnO Films By Aqueous Solution And The Influence Of Li~+, Citrate On The Growth Of ZnO Films

ZnO is a newⅡ-Ⅵwide band gap semiconductor with a hexagonal wurtzite structure. ZnO has the band gap energy of 3.37eV at 300K and a large exciton binding energy (60meV), which makes it the promising materials for UV light-emitting devices. ZnO films also have some other potential applications such as transparent conductors, UV photodetectors, piezoelectric devices and gas sensors, etc. The renewed interest of ZnO film is fueled since room temperature lasing was reported by Tang et al.In this paper, high quality of ZnO films were deposited on silicon and pre-treated sapphire substrates successfully by a two-step aqueous solution routes. X-ray diffraction, room temperature photoluminescence (PL), reflection spectrum and scanning electron microscopy(SEM) were applied to analyze the microstructure, optical properties, surface morphology of the ZnO films. The results are summarized as follow:1. High quality ZnO films are grown on ZnO-buffered c-plane sapphire substrates at a low temperature of 70℃by a two-step aqueous solution process. The ZnO buffer was deposited on the pre-treated sapphire substrate by RF reactive magnetron sputtering or pulsed laser deposition(PLD). The treatment methods of sapphire include the acid etching, nitridation and oxidation. XRD scan and phi-scan results show the films are highly (001) textured and have epitaxial relationship with the substrates. Sapphire treatment, such as acid etching, nitridation and oxidation can influence the nucleation of the film growth, and the buffer layer determines the crystalline quality of the ZnO films. The maximum PL quantum efficiency of ZnO films grown with hydrothermal method is found to be about 80% of single-crystal ZnO.2. ZnO thin films are prepared on ZnO-buffered Si(100) substrates by a two-step aqueous process.We studied the influence of Li+and trisodium citrate on the growth of ZnO films. SEM results show that the Li+ions in the solution play the role to smooth the morphology of ZnO films, resulting in the films to be uniform, continuous and compact. For the films grown in the solution with citrates, the grain size of ZnO is not changed obviously, but the growth rates of the films are reduced considerably and the PL intensity is enhanced. The reduction of the growth rate can be attributed to the citrates inhibiting ZnO from the growth.