生长条件对Ga掺杂ZnO薄膜微观结构及光致发光性能的影响

利用热氧化法在不同参数条件下生长了Ga掺杂范围较宽的ZnO薄膜, 研究了ZnO薄膜的表面微观结构和光致发光性能. 研究表明: Ga以Ga³⁺存在并掺入ZnO晶格取代Zn²⁺, Ga的掺入改变了ZnO薄膜中的缺陷类型及浓度、化学计量比、薄膜表面结晶质量, 进而影响了薄膜的光致发光性能. 随着热氧化温度升高, Ga掺杂量增大, ZnO薄膜的晶粒尺寸增大, 尺寸更均一, 紫外光与可见光强度比增大. 随着热氧化时间延长, Ga掺杂量降低, ZnO薄膜的晶粒尺寸均一性变差, 紫外光与可见光强度比减小.

Effects of growth conditions on the microstructures and photoluminescence properties of Ga-doped ZnO films

ZnO has a wide direct band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature, which is recognized as one of the promising semiconductors for optoelectronic device applications. However, ZnO generally displays visible defect-related deep-level emission and/or UV near-band-edge emission, which is strongly dependent on the growth method and condition. It has been reported that doping with IIIA elements can improve the optical properties of ZnO. Among them, Ga doping is considered not to induce large lattice distortion of ZnO due to the fact that the bonding lengths of Ga-O and Zn-O are similar and ionic radii of Ga³⁺ and Zn²⁺ are also similar. The gallium related compounds such as triethylgallium, gallium nitrate and gallium oxide are used as the Ga doping sources. It has been proved that ZnO film can be grown directly by the thermal oxidation of ZnS substrate. In this research, the Ga doping is adopted in the growth of ZnO film by applying the molten gallium to the surface of ZnS substrate and performing the subsequent thermal oxidation in the air at 650 and 700 °C for 3 and 8 h, respectively. The effects of growth condition on the microstructures and photoluminescence properties of the Ga-doped ZnO film are investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and photoluminescence at room temperature. In addition, the relationship among the oxidation temperature, oxidation time, Ga doping content and photoluminescence properties is discussed. The results show that the Ga-doped ZnO films grown under different growth conditions exhibit various amounts of Ga content and the gallium is present in the ZnO matrix as Ga³⁺ by partially substituting Zn²⁺. The Ga doping affects the microstructure and photoluminescence property by changing the defect type and level, stoichiometric ratio, and crystal quality of ZnO film. As the oxidation temperature increases, the amount of Ga doping content increases. In addition, the grain size of the Ga-doped ZnO film increases and becomes uniform, and the ratio of ultraviolet emission intensity to visible emission intensity increases. However, as the oxidation time increases, the amount of Ga doping content decreases, the grain size of the Ga-doped ZnO film becomes non-uniform, and the ratio of ultraviolet emission intensity to visible emission intensity decreases.