Melting point of Sn as the optimal growth temperature in realizing the favored transparent conducting properties of In2O3:Sn films

Highlights: • At T_S ∼ T_Sn (Sn melting point) rapid dopant inclusion causes sharp rise in $\mu$, drop in $\rho$, spread in $E_g$, ascent in F-Merit ($\text{Φ}$). • At T_S > T_Sn Urbach energy enhances due to dopant induced defects, $\text{Φ}$ reduces via added optical absorption by metallic Sn. • $E_g$ vs. $n_e$^2/3 plot reveals two distinct regimes of ITO growth temperature across T_Sn. • Reduced effective mass of charge carriers ($m_{vc}^{\ast })$ increases by 0.072$m_0$ due to fast dopant incorporation across T_Sn. • T_Sn identifies a optimal growth temperature in attaining favorable TCO properties in ITO films. At substrate temperature (T_S) close to melting point of Sn (T_Sn) rapid incorporation of metallic dopants in significant amount introduces sharp rise in mobility ($\mu$) and concentration ($n_e$) of charge carriers, leading to substantial reduction in resistivity (ρ); simultaneous sharp widening in optical gap ($E_g$) results in optimum Figure-of-Merit (Φ). The $E_g$ vs. $n_e$^2/3 plot demonstrates two distinct regimes of T_S across T_Sn, leading to higher reduced effective mass of charge carriers, $m_{vc}^{\ast }$ by 0.072$m_0$ owing to rapid incorporation of Sn⁴⁺ at substitutional site of In³⁺ in In₂O₃ matrix. Consequently, the self-energy due to electron-impurity scattering rises and/or the material self-converts to an alloy-like ensemble. On further increase in T_S, Φ reduces due to enhanced optical absorption by metallic dopants and dopant induced defects, as noted by enhanced Urbach-energy ($E_U$). Rather than any arbitrary T_S, T_Sn has been demonstrated as an optimal growth temperature for ITO films grown by RF magnetron sputtering.