Structural and optical properties of nanocrystalline Er2O3 thin films deposited by a versatile low-pressure MOCVD approach

Nanocrystalline Er2O3 thin films have been grown on Si(100) by low-pressure metallorganic chemical vapor deposition in the temperature range of 450-700°C using the tris(isopropylcyclopentadienyl)erbium precursor and O-2. The growth kinetics has been investigated in real time using laser reflectance interferometry as a function of growth parameters, and three different steps have been highlighted: (i) the incubation, (ii) the nucleation, and (iii) the growth stages. It is demonstrated that functionalization of the Si substrate surface is important for shortening the incubation time and, consequently, reducing subcutaneous oxidation of the Si substrate and for preventing nonhomogeneous nucleation that yields rough films. The growth kinetics has been correlated with film properties. X-ray diffraction patterns show strongly (111) oriented Er2O3 thin films even at temperature as low as 400 degrees C; however, a deposition temperature of 600 degrees C is optimal for obtaining films with highest refractive index and lowest surface roughness (root-mean-square = 0.4 nm). Transmission electron microscopy shows very sharp interfaces and compact films. Spectroscopic ellipsometry analysis of the optical properties shows a very high refractive index comparable to that of Er2O3 single crystal and a very high transparency in the visible-ultraviolet energy photon range.