Substrate temperature modulated optical characterizations of α-CdIn₂Se₄ thin films grown by pulsed laser deposition technique

The current study examines the effect of substrate temperature (<i>T</i> _s) on the optical characteristics of CdIn₂Se₄ thin films grown by the pulsed laser deposition technique using a UV-Vis-NIR spectrophotometer. Transmittance maxima of CdIn₂Se₄ thin films shift with a change in <i>T</i> _s, exhibit high absorption in the visible region, and depict an absorption coefficient (<i>α</i>) of ≃10⁷ m^-1. Refractive index spectra of CdIn₂Se₄ thin films controlled by <i>T</i> _s reflect crests at characteristic wavelengths (<i>λ</i> _c) and a wavelength (<i>λ</i>) higher than <i>λ</i> _c; spectra display normal dispersion. The extinction coefficient (<i>k</i>) of <i>T</i> _s tempered CdIn₂Se₄ thin films decreases as <i>λ</i> increases and reaches a minimum at <i>λ</i> _c; the contribution of free carrier absorption can explain the increase in <i>k</i> values after <i>λ</i> _c. The effect of <i>T</i> _s on the optical band gap energy (<i>E</i> _g) of the CdIn₂Se₄ thin films is discussed. For <i>T</i> _s-modulated CdIn₂Se₄ thin films, dielectric constants, loss tangent, Urbach energy, Urbach absorption coefficient, and optical and electrical conductivities have been inferred. Peak values of the volume and surface energy loss functions of CdIn₂Se₄ thin films were retrieved. A Fourier transform infrared spectrophotometer verified the purity of CdIn₂Se₄ thin films formed at different <i>T</i> _s. The current study indicates that CdIn₂Se₄ thin films are promising options for designing and developing upcoming high-efficiency opto-electronic devices. Implications are discussed.