Microstructure, phase transition, and interfacial chemistry of Gd ₂O ₃/Si(111) grown by electron-beam physical vapor deposition

The effects of growth temperature, film thickness, and oxygen flux on the microstructure, phase transition, and interfacial chemistry of gadolinium oxide (Gd ₂O ₃) films grown on Si(111) substrates by electron-beam physical vapor deposition were investigated using a combination of transmission electron microscopy (TEM), electron diffraction, scanning TEM, x-ray energy dispersive spectrometry, and electron energy loss spectrometry. The authors find that a low growth temperature (250 °C) and a high oxygen flux (200 sccm) led to a small grain size and a high porosity of the Gd ₂O ₃ film. Lowering the oxygen flux to 50 sccm led to reduced film porosity, presumably due to the increased diffusion length of the Gd atoms on the surface. Increasing the growth temperature to 650 deg:C resulted in a film with large columnar grains and elongated pores at the grain boundaries. Thin films grown at 250 C consisted of cubic Gd ₂O ₃, but thermodynamically less stable monoclinic phase formed as the film thickness increased. Lowering the oxygen flux apparently further promoted the formation of the monoclinic phase. Furthermore, monoclinic phase dominated in the films grown at 650 °C. Such phase transitions may be related to the stress evolution of the films at different temperatures, thicknesses, and oxygen fluxes. Enhanced Gd ₂O ₃/Si interfacial reaction was observed as the growth temperature, film thickness, and oxygen flux increased. Moreover, oxygen was found to play a crucial role in the Gd ₂O ₃/Si interfacial reaction and the formation of Gd-Si-O interface layers, which proceeded by the reaction of excess oxygen with Si followed by the intermixing of SiO _x and Gd ₂O ₃.