Systematic analysis of optical constants in IGZO thin films under controlled oxygen partial pressure and working pressure

초록

This study investigates the optical properties of nine indium gallium zinc oxide thin films deposited under three oxygen partial pressures (OPP) (10%, 30%, 50%) and three working pressures (2, 5, 10 mTorr). Spectroscopic ellipsometry (SE) data were analyzed with the Cauchy-Urbach (CU) model to extract refractive index (n), extinction coefficient (k), and dielectric functions (epsilon(1), epsilon(2)). Thicknesses derived from SE agreed with stylus profiler measurements within 10%, confirming the CU model's reliability. Both n and k decreased with increasing working pressure, reflecting reduced electron density due to fewer oxygen vacancies. While n varied <1% at 623 nm across the OPP range, k and epsilon(2) were highly sensitive to oxygen incorporation, decreasing by similar to 54% at 623 nm as OPP increased from 10% to 50%. These results indicate that higher OPP and working pressures suppress oxygen-vacancy-induced sub-gap states, thereby lowering optical absorption in the visible range.

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