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

doi:10.15541/jim20150148

Abstract

Abstract:

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 N₂atmosphere 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.

Key words: CdxTe thin films, co-evaporation, CdTe solar cells

CLC Number:

TQ174

SHU Qing, WU Li-Li, FENG Liang-Huan, WANG Wen-Wu, CAO Wu-Xing, ZHANG Jing-Quan, LI Wei, LI Bing. Preparation and Characterization of Cd_xTe Thin Films Deposited by Co-evaporation[J]. Journal of Inorganic Materials, 2015, 30(10): 1099-1104.

Figures/Tables 7

Table 1 The Cd/Te ratio of as-deposited CdxTe thin film

Theoretical x₀	Actual x₁	x₁/x₀
0.2	0.2260	1.130
0.4	0.4500	1.125
0.6	0.6499	1.083
0.8	0.8812	1.102

Fig. 1 XRD patterns of as-deposited CdxTe thin films (x=0.2, 0.4, 0.6, 0.8)

Fig. 2 XRD patterns of CdxTe thin films annealed at 185℃(x=0.2, 0.4, 0.6, 0.8)

Fig. 3 Morphology of CdxTe thin films observed by SEM images immediately after deposition (a-d) and annealing at 185℃(e-h)

Fig. 4 UV-visible absorption spectra of different CdxTe thin films. UV-visible absorption spectra of different CdxTe thin films. (a) Cd0.2Te , Cd0.4Te , Cd0.6Te , Cd0.8Te , as-deposited; (b) Cd0.2Te , Cd0.4Te , Cd0.6Te , Cd0.8Te and annealed at 185℃

Fig. 5 Energy band gap (Eg) of different CdxTe thin films

Fig. 6 Temperature dependence of dark conductivity of different CdxTe thin films (Cd0.2Te , Cd0.4Te , Cd0.6Te , Cd0.8Te and as-deposited)

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