Yttrium oxide thin film deposition by atomic layer epitaxy (ALE) was studied at 200±425 C using Y(thd) 3 , Y(thd) 3 (bipyridyl), or Y(thd) 3 (1,10-phenanthroline) (thd = 2,2,6,6-tetramethyl-3,5-heptanedione) as an yttrium precursor, and ozone as an oxygen source. All yttrium precursors were analyzed by thermogravimetry/differential thermal analysis (TG-DTA) and mass spectrometry (MS). Soda lime glass and Si(100) were used as substrates. With all precursors, a constant deposition rate of 0.22±0.23 (cycle) ±1 was observed at 250±350 C on both substrates, indicating a surface-controlled growth and similar surface species at the deposition temperatures used. The effect of growth parameters, such as reactant pulsing times, was investigated in detail at 350 C using Y(thd) 3 . Deposited films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM) in order to determine crystallinity and surface morphology, while ion-beam analysis and X-ray photoelectron spectroscopy (XPS) were used to analyze stoichiometry and impurity levels. Infrared (IR) measurements were performed to determine the type of carbon impurity. Crystalline films with a (400) dominant orientation were obtained when depositions were carried out within the ALE window (temperature range of 250±375 C), but films deposited below 250 C were nearly amorphous. Preferential orientation changed from (400) to ( 222) when deposition temperatures were raised slightly above the ALE window to 375 C, where a partial decomposition of Y(thd) 3 probably takes place. Judging from the impurity levels of the films and growth rates, the adducting of Y(thd) 3 does not bring about any advantages in the ALE growth of Y 2 O 3 .