Growth and Structural Characteristics of CuGaSe₂ Films Fabricated from Metallic Precursors Followed by an Elemental Se Reaction Process

We investigated the growth, structural and optical characteristics of CuGaSe₂ thin films prepared with the selenium reaction. Metallic precursor layers from Cu_0.5Ga_0.5 and Cu_0.8Ga_0.2 alloy targets were prepared on a sodalime glass substrate by using DC magnetron sputtering, and then annealed to form CuGaSe₂ in a rapid thermal process (RTP) with selenium radicals generated by a thermal cracker. The base and sputtering pressures were < 5×10⁻⁷ Torr and 30 mTorr, respectively. At ambient temperature, the precursors from the Cu_0.5Ga_0.5 and Cu_0.8Ga_0.2 targets were deposited at the rates of 42 nm/min. and 45 nm/min., respectively. The film thicknesses were about 300 nm. Selenization was carried out at different annealing temperatures of T _a = 450 °C, 500 °C, 550 °C, and 600 °C for time periods of 15 min., 30 min., and 60 min. We found that high quality CuGaSe₂ films of crystal grains (∼1 μm in dia.) fabricated with a reaction using elemental Se at temperatures as low as 450 °C for 30 min. When T _a ≤ 350 °C, the Se reaction was insufficient to form CuGaSe₂. However, the annealing time had little effect on the formation of CuGaSe₂ at T _a ≥ 450 °C. For all the samples, the photoluminescence (PL) emission was only from the donor–acceptor interband transition D1A1 for all the composition ratios of the films [Ga]/[Cu] ∼1.