Effect of Preparation Conditions on the Fundamental Absorption Edge of Y2O3 Thin Films

The fundamental absorption edge of Y 2 O 3 thin fi lms obtained by discrete evaporation and high-frequency (HF) onplasma sputtering in various atmospheres was studied using optical spectroscopy. It was ascertained that the optical bandgap Eg increased from 5.65 eV for Y 2 O 3 fi lms obtained by discrete evaporation to 5.77 eV for fi lms obtained by HF sputtering in Ar to 5.90 eV for fi lms obtained by HF sputtering in O 2 . The effective reduced mass of free charge carriers was estimated. It was found that the concentration of free charge carriers in Y 2 O 3 fi lms obtained by ionplasma sputtering in Ar with 50% O 2 was N = 1.34·1017 cm –3 whereas sputtering in 100% O 2 gave N = 1.38·10 18 cm –3 , which was typical of degenerate semiconductors. It was shown that the shift of the fundamental absorption edge in Y 2 O 3 thin fi lms after addition of O 2 to the sputtering atmosphere was most likely caused by the Burstein–Moss effect.