Optical Properties of Reactive RF Magnetron Sputtered Polycrystalline Cu3N Thin Films Determined by UV/Visible/NIR Spectroscopic Ellipsometry: An Eco-Friendly Solar Light Absorber

Abstract

Copper nitride ((Formula presented.)), a metastable poly-crystalline semiconductor material with reasonably high stability at room temperature, is receiving much attention as a very promising next-generation, earth-abundant, thin film solar light absorber. Its non-toxicity, on the other hand, makes it a very attractive eco-friendly (greener from an environmental standpoint) semiconducting material. In the present investigation, (Formula presented.) thin films were successfully grown by employing reactive radio-frequency magnetron sputtering at room temperature with an RF-power of 50 W, total working gas pressure of (Formula presented.), and partial nitrogen pressures of (Formula presented.) and (Formula presented.), respectively, onto glass substrates. We investigated how argon affected the optical properties of the thin films of Cu (Formula presented.) N, with the aim of achieving a low-cost solar light absorber material with the essential characteristics that are needed to replace the more common silicon that is currently in present solar cells. Variable angle spectroscopic ellipsometry measurements were taken at three different angles, (Formula presented.), (Formula presented.), and (Formula presented.), to determine the two ellipsometric parameters psi, (Formula presented.), and delta, (Formula presented.). The bulk planar (Formula presented.) layer was characterized by a one-dimensional graded index model together with the combination of a Tauc–Lorentz oscillator, while a Bruggeman effective medium approximation model with a (Formula presented.) air void was adopted in order to account for the existing surface roughness layer. In addition, the optical properties, such as the energy band gap, refractive index, extinction coefficient, and absorption coefficient, were all accurately found to highlight the true potential of this particular material as a solar light absorber within a photovoltaic device. The direct and indirect band gap energies were precisely computed, and it was found that they fell within the useful energy ranges of (Formula presented.) – (Formula presented.) eV and (Formula presented.) – (Formula presented.) eV, respectively. The atomic structure, morphology, and chemical composition of the Cu (Formula presented.) N thin films were analyzed using X-ray diffraction, atomic force microscopy, and energy-dispersive X-ray spectroscopy, respectively. The Cu (Formula presented.) N thin layer thickness, profile texture, and surface topography of the (Formula presented.) material were characterized using scanning electron microscopy.