STRAIN-INDUCED DIELECTRIC CONSTANT ENHANCEMENT OF EPITAXIAL Gd₂O₃

In modern nanoelectronics, the trend of minimization of devices led to a need for novel insulators with high dielectric constant. One of the approaches for realizing such high-k insulators for metal oxide semiconductor (MOS) based devices is the use of single crystalline rare earth oxides. These oxides present high dielectric constants, good insulating properties and can be deposited on a wide variety of substrates, including group IV and III-V semiconductors, as epitaxial thin films.

This work concentrates on Gd­₂O₃ as a gate oxide, when deposited on Si and Ge. when Gd­₂O₃ is grown epitaxially on different substrates, its structure might be modified differently to accommodate these substrates. It was found that the dielectric constant of the film is highly thickness dependent when deposited on Si. At thicknesses of 4-5nm the film presents a massive dielectric constant enhancement of up to 40% from its bulk value that is diminished gradually down to the bulk value at 10nm. When using Ge as substrate such an enhancement is not observed.

Using extensive x ray diffraction (XRD) analysis it was found that at low thicknesses, films grown on Si present a lattice distortion that is far larger than the one that is feasible to be created by the growth constraints given by the Si lattice. In contrast, when deposited on Ge and at high thicknesses the film presents a relaxed cubic lattice.

It was found that the source of the lattice distortion and the dielectric enhancement is the formation of a strain-induced metastable phase that is present in the Gd­₂O₃ film when constrained by the Si lattice.