Pulsed-laser deposition and characterization of CuIn1−xMxSe2 (M=Cr, V, and Ti) films

The films of doped chalcopyrite semiconductor, i.e. CuIn1−xMxSe2 (M=Cr, V and Ti), were grown on the soda lime glass substrates by pulsed laser deposition (PLD). The deposition was carried out with a single sintered target, which contained all the elements. X-ray diffraction of the films deposited at room temperature (RT) showed only the reflection lines from the chalcopyrite phase. However, Raman spectroscopy revealed two extra weak peaks, which might be identified with the secondary phase CuSe or a segregation of another chalcopyrite phase with different compositions. The film crystallinity and the homogeneity of composition were improved by the post-deposition annealing at 400 °C, after which the grain size was increased from 3 nm to 19 nm and the above two weak Raman peaks disappeared. Hall-effect measurements indicated that all the films were p-type semiconductors and the doped films had lower carrier concentration but higher mobility. Optical absorption measurements showed that the bandgap of doped films was increased, varying from 1.06 eV in undoped CuInSe2 to around 1.20–1.36 eV in CuIn1−xMxSe2. Compared to the well-known CuIn1−xGaxSe2 (i.e. Ga doping), the dopants studied in this work were much more effective to increase the bandgap of CuInSe2.