Control of Se layer thickness in two-step selenization and sulfurization of CuGa/In/Se precursors

Sputter-deposited bilayer CuGa/In precursors were coated by a Se layer with a different thickness from 0.5 to 1.5 μm to yield glass/Mo/CuGa/In/Se structure. Selenization of the precursors with a 0.5 μm-thick Se layer resulted in partial selenization with a relatively uniform distribution of Ga, whereas Cu(InGa)Se2 formed from 1.0 and 1.5 μm-thick Se layers showed complete selenization but with Ga accumulation at the bottom. Partial selenization of the Se-coated metal precursors by a 0.5 μm-thick Se layer was confirmed to yield better incorporation of S and effective re-distribution of Ga to form Cu(InGa)(Se,S)2 films with homogenous depth profiles of Ga and S.