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<p>Thin films of HfO<sub>2</sub> and Ge-doped HfO<sub>2</sub> were synthesized via magnetron sputtering onto Si substrates and subsequently annealed in an inert atmosphere. The evolution of their optical properties was investigated using spectroscopic ellipsometry and FTIR spectroscopy. Undoped HfO<sub>2</sub> films exhibit stable refractive indices across a wide temperature range, indicating structural density and phase stability. In contrast, Ge-doped films phase stability. In contrast, Ge-doped films in as-deposited state shows that Ge incorporation modifies the local bonding environment, giving rise to Ge–O and mixed Ge–O–Hf vibrational modes that overlap with Hf–O phonons. An annealing treatment of these films stimulates a temperature-dependent transformation in both refractive index and vibrational spectra, being remarkable at 700–900&#xa0;°C and resulted in phase separation, GeO<sub>x</sub> formation, and partial crystallization of the HfO<sub>2</sub> phase. At annealing temperatures above 700&#xa0;°C, Ge redistribution or clustering occurs also. At 900&#xa0;°C, a sharp decrease in refractive index and the emergence of monoclinic HfO<sub>2</sub> FTIR signatures suggest Ge desorption via GeO volatilization and matrix crystallization. The combined use of ellipsometry and FTIR spectroscopy enabled non-destructive monitoring of compositional and structural changes, offering insights into the thermal behavior of high-k dielectric nanocomposites. These findings support the potential application of Ge-doped HfO<sub>2</sub> films in optoelectronic devices.</p> Graphical abstract <p></p>

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Evolution of optical characteristics of HfO2 and Ge-doped HfO2 thin films upon thermal treatment in inert atmosphere

  • 期刊论文

  • 发表日期：

    2026年4月6日

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  • D. Khomenkov,
  • L. Melnichuk,
  • F. Gourbilleau,
  • L. Khomenkova,
  • O. Melnichuk

摘要

Thin films of HfO2 and Ge-doped HfO2 were synthesized via magnetron sputtering onto Si substrates and subsequently annealed in an inert atmosphere. The evolution of their optical properties was investigated using spectroscopic ellipsometry and FTIR spectroscopy. Undoped HfO2 films exhibit stable refractive indices across a wide temperature range, indicating structural density and phase stability. In contrast, Ge-doped films phase stability. In contrast, Ge-doped films in as-deposited state shows that Ge incorporation modifies the local bonding environment, giving rise to Ge–O and mixed Ge–O–Hf vibrational modes that overlap with Hf–O phonons. An annealing treatment of these films stimulates a temperature-dependent transformation in both refractive index and vibrational spectra, being remarkable at 700–900 °C and resulted in phase separation, GeOx formation, and partial crystallization of the HfO2 phase. At annealing temperatures above 700 °C, Ge redistribution or clustering occurs also. At 900 °C, a sharp decrease in refractive index and the emergence of monoclinic HfO2 FTIR signatures suggest Ge desorption via GeO volatilization and matrix crystallization. The combined use of ellipsometry and FTIR spectroscopy enabled non-destructive monitoring of compositional and structural changes, offering insights into the thermal behavior of high-k dielectric nanocomposites. These findings support the potential application of Ge-doped HfO2 films in optoelectronic devices.

Graphical abstract