Study On The Preparation And Ion Implantation Of ZnO-based Films By Sol-gel Process

Zinc oxide (ZnO), an important II—VI semiconductor with a variety of good physical and chemical properties compared with conventional wide bandgap semiconductors such as GaN, ZnSe and SiC, is suitable for many applications like transparent conductors, lasers, UV detectors, and solar cells. The main obstacle to the development of ZnO has been the lack of reproducible and low-resistivity p-type ZnO. Though nitrogen has been believed to be most promising acceptor to dope p-type ZnO, low solubility in ZnO and deep impurity level cause significant resistance to the formation of shallow acceptor level and high acceptor concentration. Co-doping method was proposed to overcome these problems and has been widely accepted in experiments.In this paper, we had prepared ZnO:Al and ZnO:Mg thin films by sol-gel process and doped high-dose N ions into ZnO:Al and ZnO:Mg films by ion implantation technique which has been widely accepted in semiconductor industry. Based on the above experiments, we had obtained results as follows:1. Influences of Al doping concentration and annealing temperatures on the structural, optical and electrical properties were investigated. Results showed that the intensities of (002) diffraction peak and excitonic near band edge emission were increased with increasing doping concentration, while defect related emission was decreased. Results calculated from Kramers-Kronig relationship showed that the absorption coefficients and refractive indexes of ZnO:Al films were decreased with increasing Al doping concentration. With increasing annealing temperatures from 600-950℃, the absorption coefficients and refractive indexes of ZnO:Al films in the visible region increased, while decreased in the ultraviolet region. In addion, the absorption edge of ZnO:Al films blueshifted with increasing annealing temperatures from 600-750℃, while redshifted when the annealing temperature exceeded 750℃. The optical absorption of ZnO:Al films in the visible region decreased with increasing annealing temperature, while increased in the ultraviolet region. Near band edge emission increased with increasing annealing temperature, but defect-related deep-level emission decreased.2. Effects of Zn, Ge ion implantation and post-thermal annealing on the structural and optical properties of ZnO films were investigated. Results showed that the diffraction peaks and photoluminescence of ZnO films evidently decreased after Zn and Ge ion implantation. The optical absorption in the visible region increased after ion implantation. Post-thermal annealing had great influences on the structural and optical properties of ZnO films. With increasing annealing temperature, the structural and optical properties of ZnO films recovered. For Zn-implanted ZnO films, the structural properties recovered after annealing at 700℃for 1 h and photoluminescence recovered after annealing at 600℃for 1 h. For Ge-implanted samples, the structural properties of ZnO films recovered after annealing at 600℃for 1 h, and the photoluminescence recovered after annealing at 800℃for 1 h.3. Effects of N-ion-implantation and annealing temperature on the structural, optical and electrical properties of ZnO:Al and ZnO:Mg films were investigated. Al contents played a very important role in preparation of p-type ZnO. Our experimental results showed that only those samples with Al/Zn=1% turned into p-type conduction. After annealing at 600℃for 30 min, Hall measurement results showed that the carriers' concentration and mobility were 1.6×10¹⁸cm^-3 and 3.76cm²/V·s, respectively. Post-thermal annealing had pronounced influences on the structural and optical properties of ZnO:(Al, N) and ZnO:(Mg, N) films. Annealing results showed that the structural and optical properties of ZnO:(Al, N) recovered after annealing at 600℃for 30 min. For ZnO:Mg films, we found evident decomposition and evaporation behavior during annealing at 600-900℃. Four-point probe resistivity measurements showed that ZnO:(Mg, N) films exhibited high resistivity after annealing at different temperatures.