退火温度对ZnS/PS薄膜的晶体结构和光电性质的影响

Influence of annealing temperature on film crystalline structure and optoelectronic properties of ZnS/PS

用脉冲激光沉积法(PLD)在多孔硅(PS)衬底上生长ZnS薄膜,分别在300℃、400℃和500℃下真空退火。用X射线衍射(XRD)和扫描电子显微镜(SEM)研究了退火对ZnS薄膜的晶体结构和表面形貌的影响,并测量了ZnS/PS复合体系的光致发光(PL)谱和异质结的I-V特性曲线。研究表明,ZnS薄膜仅在28.5°附近存在着(111)方向的高度取向生长,由此判断薄膜是单晶立方结构的-βZnS。随着退火温度的升高,-βZnS的(111)衍射峰强度逐渐增大,且ZnS薄膜表面变得更加均匀致密,说明高温退火可以有效地促进晶粒的结合并改善结晶质量。ZnS/PS复合体系的PL谱中,随着退火温度升高,ZnS薄膜的自激活发光强度增大,而PS的发光强度减小,说明退火处理更有利于ZnS薄膜的发光。根据三基色叠加的原理,ZnS的蓝、绿光与PS的红光相叠加,ZnS/PS体系可以发射出较强的白光。但过高的退火温度会影响整个ZnS/PS体系的白光发射。ZnS/PS异质结的I-V特性曲线呈现出整流特性,且随着退火温度的升高其正向电流增加。

ZnS films are deposited on porous Si（PS） substrates by pulsed laser deposition（PLD）,and the samples are annealed at 300 ℃,400 ℃ and 500 ℃ in vacuum respectively.The X-ray diffraction（XRD） and scanning electron microscope（SEM） are employed to analyze the effect of annealing on the crystalline structure and surface morphology of ZnS films.The photoluminescence（PL） spectra of ZnS/PS and I-V characteristics of the heterojunctions are also studied.The results show that highly oriented films are prepared with only one sharp XRD peak at 2θ=28.5° corresponding to βZnS（111） crystalline orientation.With the increase of annealing temperature,the intensity of（111） diffraction peak increases,and the surface of ZnS films becomes more uniform and compact which indicates that higher annealing temperature can increase the grain size and improve the crystal quality of ZnS films.In the PL spectra of ZnS/PS,the intensity of self-activated luminescence of ZnS increases while the luminescence intensity of PS decreases with the rise of annealing temperature,which indicates that annealing treatment may improve the emission efficiency of ZnS films.According to the principle of tricolor overlay,the blue and green emission from ZnS are combined with the red emission from PS,so,ZnS/PS systems could exhibit intensive white light emission.But too high annealing temperature will affect the white light emission of ZnS/PS systems.The I-V characteristics of ZnS/PS heterojunctions exhibit rectifying behavior,and the forward current increases with the rise of annealing temperature.