In the current work, CuAlSe2 alloys were fabricated by melting the stoichiometric weights of Cu, Al, and Se in a sealed quartz ampoule at a vacuum of about 3×10-2 mbar. The alloy is applied to a soda lime glass substrate, heated to various temperatures, and then thermally evaporated at a pressure of roughly 10-6 mbar. The thin layer has a thickness of 1200±100 Å. Thin films were polycrystalline with sphalerite structure but the bulk showed chalcopyrite structure throughout. An increase in the optical energy gap with substrate temperature and direct transitions in the thin layer were observed in the optical experiments. As the annealing period was raised to two hours, the films annealed at 200-400°C indicated an increase in the energy gap
