Optimization of Se layer thickness in Mo/CuGa/In/Se precursor for the formation of Cu(InGa)Se2 by rapid thermal annealing

Bilayer CuGa/In precursors were deposited on low-alkali, high-strain-point glass with a thickness of 1.8 mm by in-line DC-magnetron sputtering of CuGa (24 Ga wt%) and pure In targets. Se layers of different thicknesses, e.g., 1, 3, 5, and 8 μm, were coated on the sputter-deposited glass/Mo/CuGa/In precursors with no external heating by evaporating Se in a high vacuum evaporator. Possible reaction pathways to Cu(InGa)Se2 formation from glass/Mo/CuGa/In/(Se) precursors were suggested on the basis of the high-temperature X-ray diffraction analysis. It is also proposed that the high temperature ramp rates might be preferred for the improved Ga diffusion toward the sample surface and thus reduced phase separation between CuInSe2 and Cu(InGa)Se2. In the rapid thermal process system used in this study, the Se thickness of 3 μm demonstrated the best Ga incorporation during the selenization of 600 nm-thick CuGa/In precursors at 550–570 °C.

► Reaction pathways to Cu(InGa)Se2 from glass/Mo/CuGa/In/(Se) were suggested.
► High temperature ramp rates improved Ga diffusion during selenization of CuGa/In.
► 3 μm-thick Se layer showed the best Ga incorporation during selenization of CuGa/In.