Solar cell techniques using I-III-VI2 chalcopyrite semiconductors have made rapid progress for the solution of environmental and resources problems. Among chalcopyrite semiconductors, CuInS2 compound may be the most promising material for photovoltaic applications due to the band-gap energy of 1.5 eV which perfectly matches the solar spectrum for energy conversion.
In our previous work [1,2], non-doped and Sb-doped CuInS2 films were grown by a vacuum evaporation method. After the evaporation, these samples were subsequently annealed in air. X-ray diffraction (XRD) spectra indicated that polycrystalline CuInS2 films were successfully obtained by annealing above 200 °C. However, all the CuInS2 films showed n-type conductivity due to the sulfur deficiencies.
In this work, CuInS2 thin films were prepared by the vacuum evaporation method with an H2S annealing. After the vacuum evaporation, the samples were subsequently annealed under air or H2S atmospheres from 100 to 500 °C. The samples were examined by XRD, electron probe microanalysis (EPMA), scanning electron microscopy (SEM) and Hall measurement.
The XRD spectra indicate that the CuInS2 polycrystalline films were successfully obtained by annealing above 200 °C. We found that the films became close to stoichiometry with increasing annealing temperature under H2S atmosphere. Furthermore, it is found that maximum grain size of the samples was about 1µm from the SEM photographs. The carrier concentrations and the resistivities of the films were changed in the range of 1018-1023 cm-3 and 10-3-100 Ωcm, respectively, at room temperature and all the samples annealed in H2S indicated p-type conduction by the Hall measurement. It is deduced that the almost sulfur vacancy in the films annihilated by the H2S annealing.
[1] Y. Akaki et al, J. Phys. Chem. Solids, 64 (2003) 1863.
[2] Y. Akaki et al, Phys. Stat. Sol,(c) 3 (2006) 2597.
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