A review of molecular beam epitaxy of ferroelectric BaTiO3 films on Si, Ge and GaAs substrates and their applications

SrTiO3 epitaxial growth by molecular beam epitaxy (MBE) on silicon has opened up the route to the monolithic integration of various complex oxides on the complementary metal-oxide-semiconductor silicon platform. Among functional oxides, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip. We review the growth by MBE of the ferroelectric compound BaTiO3 on silicon (Si), germanium (Ge) and gallium arsenide (GaAs) and we discuss the film properties in terms of crystalline structure, microstructure and ferroelectricity. Finally, we review the last developments in two areas of interest for the applications of BaTiO3 films on silicon, namely integrated photonics, which benefits from the large Pockels effect of BaTiO3, and low power logic devices, which may benefit from the negative capacitance of the ferroelectric. © 2015 National Institute for Materials Science161711sciescopu

Atomic-layer deposited thulium oxide as a passivation layer on germanium

A comprehensive study of atomic-layer deposited thulium oxide (Tm2O3) on germanium has been conducted using x-ray photoelectron spectroscopy (XPS), vacuum ultra-violet variable angle spectroscopic ellipsometry, high-resolution transmission electron microscopy (HRTEM), and electron energy-loss spectroscopy. The valence band offset is found to be 3.05 ± 0.2 eV for Tm2O3/p-Ge from the Tm 4d centroid and Ge 3p3/2 charge-corrected XPS core-level spectra taken at different sputtering times of a single bulk thulium oxide sample. A negligible downward band bending of ∼0.12 eV is observed during progressive differential charging of Tm 4d peaks. The optical band gap is estimated from the absorption edge and found to be 5.77 eV with an apparent Urbach tail signifying band gap tailing at ∼5.3 eV. The latter has been correlated to HRTEM and electron diffraction results corroborating the polycrystalline nature of the Tm2O3 films. The Tm2O3/Ge interface is found to be rather atomically abrupt with sub-nanometer thickness. In addition, the band line-up of reference GeO2/n-Ge stacks obtained by thermal oxidation has been discussed and derived. The observed low reactivity of thulium oxide on germanium as well as the high effective barriers for holes (∼3 eV) and electrons (∼2 eV) identify Tm2O3 as a strong contender for interfacial layer engineering in future generations of scaled high-κ gate stacks on Ge

Atomic characterization of Si nanoclusters embedded in SiO2 by atom probe tomography

Silicon nanoclusters are of prime interest for new generation of optoelectronic and microelectronics components. Physical properties (light emission, carrier storage...) of systems using such nanoclusters are strongly dependent on nanostructural characteristics. These characteristics (size, composition, distribution, and interface nature) are until now obtained using conventional high-resolution analytic methods, such as high-resolution transmission electron microscopy, EFTEM, or EELS. In this article, a complementary technique, the atom probe tomography, was used for studying a multilayer (ML) system containing silicon clusters. Such a technique and its analysis give information on the structure at the atomic level and allow obtaining complementary information with respect to other techniques. A description of the different steps for such analysis: sample preparation, atom probe analysis, and data treatment are detailed. An atomic scale description of the Si nanoclusters/SiO2 ML will be fully described. This system is composed of 3.8-nm-thick SiO layers and 4-nm-thick SiO2 layers annealed 1 h at 900°C

Kinetic Processes in the CVD of SiC from CH3SiCl3-H2 in a Vertical Hot-Wall Reactor

The chemical vapour deposition of SiC-based ceramics from the CH3SiCl3-H2 precursor is investigated on the basis of large scale experimental and theoretical approaches. The use of a vetirtical cylindrical hot-wall LPCVD reactor permits to get a wide isothemal reaction zone with a creeping laminar flow around the substrate and a largely chemical control of the kinetics, which favours a high supersaturation and a nucleation regime. A calculation of the coverage of C (111) or Si(111) planes of SiC points out the importance of the chemisorption of SiCl3 and H radicals on C atoms and of CH3 and Cl radicals on Si atoms. On the basis of kinetic experiments and of chemical and structural investigations of the deposits, several domains of conditions are defined with different rnechanisms for the formation of SiC-based ceramics. For low temperatures and low pressures, a regime of growth of stoichiometric SiC microcrystals occurs from reaction of CH3 and SiCl3 intermediates. Higher pressures in the chemical control knetic domain, favour a regime of nucleation of nanocrystals with an excess of silicon resulting from SiCl3/SiCl2 silicon precursor

HREM Characterization of Interfaces in Thin MOCVD Superconducting Films

This paper is concerned with high-Tc, superconducting compounds produced by metal-organic chemical vapour deposition. The nanostructure of different types of interfaces - yttria stabilized zirconia buffer / (1-102)-sapphire substrate, YBa2Cu3O7-x film / Y2O3 precipitates as well as YBa2Cu3O7-x film / (001)-NdGaO3, -SrTiO3, and -MgO substrates - has been investigated by high resolution electron microscopy. The orientation relationships and the corresponding layer sequences across the interfaces have been determined with the aid of computer simulations

Low pressure chemical vapor deposition of silicon oxynitride films using tetraethylorthosilicate, dichlorosilane and ammonia mixtures

This work describes the thermodynamic simulation and the experimental investigation of the chemical vapor deposition of silicon oxide and silicon oxynitride films starting from tetra-ethyl-orthosilicate (TEOS), dichlorosilane (DCS) and ammonia mixtures. The simulation reveals that the co-deposition of silicon oxynitride - silicon dioxide films is possible at 710° C and 300 mTorr if the DCS/TEOS ratio is greater than one. If the DCS/TEOS ratio is less than one, the deposited films are exclusively composed of silicon dioxide. These predictions were confirmed in corresponding experiments by using Fourier Transform Infrared spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) and Electron Energy Loss Spectroscopy (EELS) for the characterization of the obtained films

Combining HRTEM-EELS nano-analysis with capacitance-voltage measurements to evaluate high-kappa thin films deposited on Si and Ge as candidate for future gate dielectrics

International audienceAberration corrected transmission electron microscopy and electron spectroscopy are combined with electrical measurements for the quantitative description of the structural, chemical and dielectric parameters of rare earth/transition metal oxides thin films. Atomic structure near the interface and elemental profiles across the interface up to the surface of La-doped ZrO2 and Er-doped HfO2 films prepared by atomic layer deposition on Si(100) and Ge(100) are determined. Interfacial layers unavoidably form between the semiconductor substrate and the dielectric oxide after deposition and annealing. They are evidenced from a structural and chemical point of view. From the knowledge of the chemical extent of the interfacial layer and of the accumulation capacitance of the stack, it is possible to recover the dielectric constant of both the interfacial layer and the high-κ oxide layer constituting the stack using a multi-layers capacitor model approach. Oxides with permittivities higher than 30 are stabilized. Interfacial layers, silicate/germanate in composition, with permittivites, respectively, tripled/doubled compared to the one of SiO2 are evidenced

Quantitative mapping of strain and displacement fields over HR-TEM and HR-STEM images of crystals with reference to a virtual lattice

International audienceA method for the reciprocal space treatment of high-resolution transmission electron microscopy (HR-TEM) and high-resolution scanning transmission electron microscopy (HR-STEM) images has been developed. Named “Absolute strain” (AbStrain), it allows for quantification and mapping of interplanar distances and angles, displacement fields and strain tensor components with reference to a user-defined Bravais lattice and with their corrections from the image distortions specific to HR-TEM and HR-STEM imaging. We provide the corresponding mathematical formalism. AbStrain goes beyond the restriction of the existing method known as geometric phase analysis by enabling direct analysis of the area of interest without the need for reference lattice fringes of a similar crystal structure on the same field of view. In addition, for the case of a crystal composed of two or more types of atoms, each with its own sub-structure constraint, we developed a method named “Relative displacement” for extracting sub-lattice fringes associated to one type of atom and measuring atomic columns displacements associated to each sub-structure with reference to a Bravais lattice or to another sub-structure. The successful application of AbStrain and Relative displacement to HR-STEM images of functional oxide ferroelectric heterostructures is demonstrated