Thermal Transport Evolution Due to Nanostructural Transformations in Ga-Doped Indium-Tin-Oxide Thin Films

Abstract

We report on a comprehensive theoretical and experimental investigation of thermal conductivity in indium-tin-oxide (ITO) thin films with various Ga concentrations (0–30 at. %) deposited by spray pyrolysis technique. X-ray diffraction (XRD) and scanning electron microscopy have shown a structural transformation in the range 15–20 at. % Ga from the nanocrystalline to the amorphous phase. Room temperature femtosecond time domain thermoreflectance measurements showed nonlinear decrease of thermal conductivity in the range 2.0–0.5 Wm−1 K−1 depending on Ga doping level. It was found from a comparison between density functional theory calculations and XRD data that Ga atoms substitute In atoms in the ITO nanocrystals retaining Ia-3 space group symmetry. The calculated phonon dispersion relations revealed that Ga doping leads to the appearance of hybridized metal atom vibrations with avoided-crossing behavior. These hybridized vibrations possess shortened mean free paths and are the main reason behind the thermal conductivity drop in nanocrystalline phase. An evolution from propagative to diffusive phonon thermal transport in ITO:Ga with 15–20 at. % of Ga was established. The suppressed thermal conductivity of ITO:Ga thin films deposited by spray pyrolysis may be crucial for their thermoelectric applications.

Controlled Lattice Thermal Conductivity of Transparent Conductive Oxide Thin Film via Localized Vibration of Doping Atoms

“…This provides clues that the κ l increase above the specific dopant concentration is not related to metal hydroxide formation but originates from localized vibration due to the excessive dopant amount. Therefore, the localized region generated by excessive doping of ZnO and CeO 2 becomes a new pathway for heat transfer in ITO and suppresses phonon scattering by cations, leading to the increase in κ l [ 25 , 43 ].…”

“…However, an abnormal phenomenon of lattice thermal conductivity ( κ l ) increase was observed when the ZnO concentration exceeded the optimized value, despite the assumption of further progress to a randomly disordered structure proportional to the ZnO concentration. Several studies have been carried out on the increase in κ l in relation to the dopant concentration [ 25 , 26 ]. To demonstrate this paradoxical phenomenon, two hypotheses are proposed to explain the κ l increase: (1) metal hydroxide formation due to the low bond enthalpy energy of Zn and O and (2) Zn localization due to excessive impurity doping.…”

Adjusting Photoresist Curing Temperature to Eliminate Electrostatic Breakdown from Etching Residues

“…(i) Film-forming stage. Available methods include reduction of sputtering deposition power, use of a cold substrate, and doping with Ga. , These methods are able to produce amorphous ITO films, but cannot avoid recrystallization during photoresist curing treatment . (ii) Etching stage.…”

Rattling-induced suppression of thermal transport in cubic In2O3 with Sn-Ga diatomic defect

“…The maximal power factor (PF) and minimal thermal conductivity (TC) for spray-pyrolyzed films were found for the concentration of Sn and Ga ∼5-8 at. % [1][2][3][4][5][6]. Cocemasov et al have demonstrated [6] that during spray-pyrolysis at deposition temperatures 620-650 K, Sn and Ga atoms occupy the substitutional positions in the host lattice maintaining cubic Ia3 space group symmetry.…”

“…% [1][2][3][4][5][6]. Cocemasov et al have demonstrated [6] that during spray-pyrolysis at deposition temperatures 620-650 K, Sn and Ga atoms occupy the substitutional positions in the host lattice maintaining cubic Ia3 space group symmetry. Increase of Ga concentration above the optimized value of ∼8-10 at.…”