Effects of air annealing on CuInSe₂ thin films grown by molecular beam epitaxy

High quality epitaxial CuInSe₂ (CIS) films with a range of Cu/In ratios (γ) = 0.80 to approximately 2.24 grown by molecular beam epitaxy (MBE) have been post-annealed at temperatures of T_A = 200 to approximately 400 °C in both dry-air and Ar atmospheres. Changes in the structure and composition due to annealing have been investigated. The only oxide observed experimentally for both the In-rich, and the Cu-rich CIS films was In₂O₃. This is consistent with equilibrium thermodynamic calculations which indicate that In₂O₃ is the most stable solid oxide phase. During annealing some reactions are probably kinetically limited making the annealing process a function of time and temperature, but the equilibrium thermodynamic results reported here simplify interpretation of phase space.