Fabrication of n- and p-type doped CuFeSe2 thin films achieved by selenization of metal precursors

CuFeSe2 thin films have been grown by selenization of a CuFe alloy precursor. The CuFe alloy has been obtained by successive evaporation of thin Cu/Fe/Cu... layers on glass substrates heated at 550 degrees C. After deposition the metal alloy precursor is polycrystalline and there is an interdiffusion of metals all along the thickness. The atomic ratio Cu/Fe was varied from 0.8 to 1.15. The metal alloy precursor is selenized in a vacuum chamber; after heating at 550 degrees C it is exposed to selenium vapour (evaporation rate 3-4 nm s(-1) for 45 min). At the end of the process only CuFeSe2 diffraction peaks are visible in the x-ray diagram. The films exhibit a (112) preferential orientation. The scanning electron microscope (SEM) visualization of the films shows that films are composed of well-faceted grains. The Cu-rich films are slightly porous while the Fe-rich are more homogeneous. The SEM study shows that the thickness of the grains is of the same order of magnitude as that of the CuFeSe2 films. Electrical measurements have shown that Cu-rich films are n-type with a room temperature resistivity of (5-9) x 10(2) Omega cm, while Fe-rich films are p-type with a room temperature resistivity of (3-5) x 10(1) Omega cm. It is shown that the electrical properties of the films are controlled by the grain boundary scattering effect.