Electronic and structural properties of copper selenide (Cu2−xSe) thin films as determined by in-situ real-time and ex-situ characterization

Real-time spectroscopic ellipsometry (RTSE) is shown to be an effective contactless probe of copper selenide thin-films used as a precursor material during 2-stage and 3-stage growth of Cu(In,Ga)Se₂ solar cells. The Cu_2-xSe thin-films were deposited by a hybrid sputtering/evaporation process onto native oxide covered Si(100) and studied by RTSE, and by complementary atomic force microscopy (AFM), X-ray diffractometry, transmission and reflection (T&R) spectrophotometry, and Hall Effect measurements. RTSE deduction of the total charge carrier densities (n), electronic scattering times (τ), fundamental energy bad-gaps (E_g), and electrical resistivities (ρ) of the Cu_2-xSe thin-films agree well with post-deposition ex-situ measurements. The RTSE measurement reveals growth mechanism and dielectric functions which ultimately reflect the electronic behavior.