CdxTe薄膜的共蒸发法制备及其表征

采用CdTe和Te双源共蒸发的方法, 调控CdTe和Te源的蒸发速率, 首次制备出一系列不同x组分的Cd_xTe二元化合物薄膜, 并在N₂气气氛下进行185℃退火处理。通过XRD、SEM、紫外-可见吸收光谱分析及暗电导率-温度关系对Cd_xTe薄膜的结构、形貌、光学和电学性质进行表征。紫外-可见吸收光谱分析表明, 不同x组分的Cd_xTe薄膜, 其禁带宽度可在0.99~1.46 eV之间变化, 随着x值从0.8减小到0.2, 吸收边向长波方向移动, 而且透过率也显著下降。XRD结果表明, x值小于0.6时, 刚沉积的Cd_xTe薄膜为非晶相; 随着x的值逐渐靠近1, 刚沉积的薄膜明显结晶, 沿CdTe(111)方向择优生长, 退火处理促使薄膜从非晶转变为多晶。Cd_xTe薄膜的导电类型为p型, 其暗电导率随温度的上升而增大, 当温度继续升高至临界点时, 薄膜暗电导率-温度关系出现反常。这些结果表明, Cd_xTe薄膜将有望用于CdTe薄膜太阳电池以拓展电池的长波光谱响应。

Preparation and Characterization of CdxTe Thin Films Deposited by Co-evaporation

Cd_xTe thin films with different x values were deposited for the first time through controlling evaporation rates of CdTe and Te powder by vacuum co-evaporation. Then the films were annealed in N₂ atmosphere at 185℃. The morphological, structural, optical, and electrical properties of the Cd_xTe films were investigated by X ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible absorption spectrum and temperature dependence of the dark conductivity. UV-visible absorption spectrum demonstrates that energy band gaps (E_g) of different Cd_xTe films change from 0.99 eV to 1.46 eV. The absorption edges of different Cd_xTe films move towards longer wavelength and their transmittances reduce dramatically as the x value decreases from 0.8 to 0.2. XRD shows that as-deposited Cd_xTe thin films are amorphous when value of x is less than 0.6. Otherwise, Cd_xTe thin films are crystalline whose CdTe phase with preferential in (111) direction while value of x is approaching 1. The result indicates that annealing treatment is helpful for the films shifting from amorphous to polycrystalline. All the films exhibit p-type conductivity and the conductivity increases firstly as temperature rises. But it becomes abnormal while the temperature reaches a certain point. Data from this research suggest that Cd_xTe thin films can potentially be used for CdTe thin film solar cells to improve the long wavelength response.