Microstructure, phase transition, and interfacial chemistry of Gd2O3/Si(111) grown by electron-beam physical vapor deposition

Abstract

The effects of growth temperature, film thickness, and oxygen flux on the microstructure, phase transition, and interfacial chemistry of gadolinium oxide (Gd2O3) 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 Gd2O3 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 °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 Gd2O3, 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 Gd2O3/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 Gd2O3/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 SiOx and Gd2O3.

Single crystal Gd2O3epitaxially on GaAs(111)A

“…Similar thickness dependent transformation has been reported on polycrystalline Gd 2 O 3 grown by electron beamphysical vapor deposition method on Si(111); 19,31 in that case, the deposited layer consists of cubic and monoclinic mixed phases close to the film/substrate interface and becomes monoclinic far away from interface. The authors manipulated the strain state of the deposited layer by ion beam assisted deposition and concluded that compressive stress favors the formation of the denser monoclinic phase.…”

“…13,14 Cubic Gd 2 O 3 is the most common one at room temperature and a high-quality epitaxial layer with (110) surface orientation has been reported growing on various semiconductors, such as GaAs(001), 15 Si(001), 16 and Ge(001), 17 and with (111) orientation on Si(111). [18][19][20] Depending on the deposition method and growth parameters, the formation of monoclinic Gd 2 O 3 in thick films was reported in some cases. 17,19 Interestingly, Gd 2 O 3 epitaxially grown on GaN(0001) is not cubic.…”

“…[18][19][20] Depending on the deposition method and growth parameters, the formation of monoclinic Gd 2 O 3 in thick films was reported in some cases. 17,19 Interestingly, Gd 2 O 3 epitaxially grown on GaN(0001) is not cubic. With the thickness less than 4 nm, the oxides have been demonstrated to be hexagonal with (0001) normal orientation and have a high dielectric constant κ of 24 and high thermal stability even at 1100 °C.…”