I-III-VI2 chalcopyrite semiconductors have made rapid progress for the solution of environmental and resources problems. Among the chalcopyrite semiconductors, CuInS2 may be the most promising material for photovoltaic applications due to the bandgap energy of 1.5 eV which perfectly matches the solar spectrum for energy conversion.
In our previous work [1], undoped and Sb-doped CuInS2 films were grown by vacuum evaporation method. The source materials were CuInS2 powder with or without Sb atoms grown by a hot-press (HP) method. After the evaporation, these samples were annealed in air. X-ray diffraction (XRD) spectra indicated that polycrystalline CuInS2 films were successfully obtained by annealing above 200°C.
In this work, CuInS2 thin films were grown on ITO/glass substrate by vacuum evaporation method. After the vacuum evaporation, the samples were subsequently annealed under H2S or air 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. It is found that grain size increased with increasing annealing temperature. Maximum of grain size is 80 nm. Hall measurements revealed that CuInS2 thin films showed n-type conductivity. A carrier concentration, resistivity and mobility of the samples at 300°C are approximatel 1018 cm-3, 10-1 Ωcm and 20 cm2/Vs. It seemed that an origin of p-type conductivity was a lattice defect which is particularly Cu vacancy from the EPMA results.
[1] Y. Akaki et al, J. Phys. Chem. Solids, 64 (2003) 1863.
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