Preparation Of P-Type ZNO Thin Films By Sol-Gel Method

ZnO is a II-VI group, direct band gap semiconductor material. It has excellent optical, electrical and other physical properties and can be widely used in areas such as short wavelength optoelectronics, transparent electrodes, thin film transistor, various piezoelectric devices. ZnO has aroused great research interests in the field of wide band gap semiconductor materials. Realizing high quality and stable p-type ZnO material is the main issue currently limiting the production of ZnO-based devices. Theories and experiments show that through appropriate methods, doping with I or V group elements can achieve p-type ZnO materials.In this thesis, Na and P doped ZnO films were prepared by sol-gel process. The samples were analyzed by using X-ray diffraction (XRD), scanning electron microscope (SEM), ultraviolet-visible spectrophotometer (UV-vis) and Hall effect measurement to investigate the structure, surface morphology, optical and electrical properties, respectively. The effect of doping concentration and annealing temperature were discussed in this work.NaCl was chosen as the Na source for doping ZnO thin films. Results show that Na dopded films exhibit better crystallinity and are highly oriented along the (002) direction perpendicular to the substrate. All the films have tensile strain along the c-axis caused by the lattice distortion. The films prepared have the thickness between 285³06nm and the grain size near 20nm. The film doped 10at.% Na and annealed at 550℃has best crystallinity and has a high optical transmittance of over 90%. The film shows p type behavior, the resistivity, Hall mobility and the carrier concentration is 103Ω·cm, 0.385cm²·V^-1·s^-1, 1.66×10¹⁷cm^-3, respectively.Phosphorus doped ZnO films were synthesized by sol-gel method successfully with trimethyl phosphate as the doping source. When the doping concentration was 1at.%, 2at.%, 3at.%, the atom ratio of P:Zn in the film was 0.87at.%, 1.67at.%, 2.23at.%, close to the initial doping ratio, and there is no other phosphorus phase in the film. The film shows polycrystalline wurtzite structure and the grain size is about 14 to 17nm. The optical transmittance in the visible region is over 80%. The 2at.% P doped film preheated at 250℃and annealed at 500℃shows best p type electrical properties, the resistivity of film is 1.64×10³Ω·cm, Hall mobility is 0.376cm²·V^-1·s^-1 and the carrier concentration is 1.02×10¹⁶cm^-3.