玻璃上热壁真空沉积生长CdTe薄膜的结构及光学特性

Structural and Optical Properties of CdTe Thin Films on Glass Grown by Hot Wall Vacuum Deposition

采用热壁真空沉积的方法,在清洁的玻璃衬底上生长了不同膜厚的CdTe薄膜,对其结构和薄膜的本征吸收光学特性进行了测量分析研究.XRD测试显示薄膜为多晶,具有标准的立方结构,沿(111)方向有明显的择优取向.晶格常数的计算值为0.649nm,与标准值符合得较好.用Cary 5000型双光束分光光度计测试了薄膜的反射谱和透射谱,显示在本征吸收区透过率随着膜厚的增加和波长的减小而减小.对测量的反射谱和透射谱采用较严格的数学处理,计算得到了描述薄膜宏观光学特性的重要物理量,即薄膜的吸收系数、消光系数、折射率等.用(hνα)2对hν作图,得出了薄膜厚度为0.12,0.48和0.81μm的光学能隙分别为1.54,1.48和1.46eV,证实了材料是直接带隙结构,且在本征吸收的可见光区有高的吸收系数.

CdTe thin films with different thicknesses are prepared on well-cleaned glass by hot wall vacuum deposition,and their structural and optical properties are measured. XRD results show that the films are polycrystalline with a typical cubic phase structure and preferred orientation of （111）. The lattice constant is 0. 649nm for a 17. 87μm film, which matches the standard value well. The transmittance spectra and the reflection spectra are measured with a Cary 5000 double beam spectrometer from 200 to 1200nm,and both the absorption coefficient and the extinction coefficient as well as the refractive index are discussed in the intrinsic absorption region. A plot of （hνα）^2 versus hν is used to determine the optical energy gap of the CdTe thin films. It is found that the optical energy gap decreases with the increase of film thickness, possibly due to a larger grain size. These results confirm that CdTe is a direct gap material with a high absorption coefficient in the intrinsic absorption region.