Evolution of Ge wetting layers growing on smooth and rough Si (001) surfaces: isolated {105} facets as a kinetic factor of stress relaxation

The results of STM and RHEED studies of a thin Ge film grown on the Si/Si(001) epitaxial layers with different surface relief are presented. Process of the partial stress relaxation was accompanied by changes in the surface structure of the Ge wetting layer. Besides the well-known sequence of surface reconstructions ($2 \times 1 \rightarrow 2 \times N \rightarrow M \times N$ patches) and hut clusters faceted with {105} planes, the formation of isolated {105} planes, which faceted the edges of $M \times N$ patches, has been observed owing to the deposition of Ge on a rough Si/Si (001) surface. A model of the isolated {105} facet formation has been proposed based on the assumption that the mutual arrangement of the monoatomic steps on the initial Si surface promotes the wetting layer formation with the inhomogeneously distributed thickness that results in the appearance of $M \times N$ patches partially surrounded by deeper trenches than those observed in the usual Ge wetting layer grown on the smooth Si(001) surface. Isolated {105} facets are an inherent part of the Ge wetting layer structure and their formation decreases the surface energy of the Ge wetting layer.Comment: 27 pages, 8 figure

STM and RHEED study of the Si(001)-c(8x8) surface

The Si(001) surface deoxidized by short annealing at T~925C in the ultrahigh vacuum molecular beam epitaxy chamber has been in situ investigated by high resolution scanning tunnelling microscopy (STM) and reflected high energy electron diffraction (RHEED). RHEED patterns corresponding to (2x1) and (4x4) structures were observed during sample treatment. The (4x4) reconstruction arose at T<600C after annealing. The reconstruction was observed to be reversible: the (4x4) structure turned into the (2x1) one at T>600C, the (4x4) structure appeared again at recurring cooling. The c(8x8) reconstruction was revealed by STM at room temperature on the same samples. A fraction of the surface area covered by the c(8x8) structure decreased as the sample cooling rate was reduced. The (2x1) structure was observed on the surface free of the c(8x8) one. The c(8x8) structure has been evidenced to manifest itself as the (4x4) one in the RHEED patterns. A model of the c(8x8) structure formation has been built on the basis of the STM data. Origin of the high-order structure on the Si(001) surface and its connection with the epinucleation phenomenon are discussed.Comment: 26 pages, 12 figure

Evolution of Ge wetting layers growing on smooth and rough Si (001) surfaces: isolated {105} facets as a kinetic factor of stress relaxation

The results of STM and RHEED studies of a thin Ge film grown on the Si/Si(001) epitaxial layers with different surface relief are presented. Process of the partial stress relaxation was accompanied by changes in the surface structure of the Ge wetting layer. Besides the well-known sequence of surface reconstructions (2 × 1 → 2 × N → M × N patches) and hut-clusters faceted with {105} planes, the formation of isolated {105} planes, which faceted the edges of M × N patches, has been observed owing to the deposition of Ge on a rough Si/Si (001) surface. A model of the isolated {105} facet formation has been proposed based on the assumption that the mutual arrangement of the monoatomic steps on the initial Si surface promotes the wetting layer formation with the inhomogeneously distributed thickness that results in the appearance of M × N patches partially surrounded by deeper trenches than those observed in the usual Ge wetting layer grown on the smooth Si(001) surface. Isolated {105} facets are an inherent part of the Ge wetting layer structure and their formation decreases the surface energy of the Ge wetting layer

Structure, Oxygen Content and Electric Properties of Titanium Nitride Electrodes in TiN_x/La:HfO₂/TiN_x Stacks Grown by PEALD on SiO₂/Si

This work reports experimental results of the quantitative determination of oxygen and band gap measurement in the TiNx electrodes in planar TiNx top/La:HfO2/TiNx bottom MIM stacks obtained by plasma enhanced atomic layer deposition on SiO2. Methodological aspects of extracting structural and chemical information from (scanning) transmission electron microscopy imaging (bright field and high angular annular dark field), energy dispersive X-ray spectrometry and electron energy loss spectroscopy are thoroughly considered. The study shows that the oxygen concentration is higher in the TiNxOy bottom electrode (about 14.2 ± 0.1 at. %) compared to the TiNxOy top electrode (about 11.4 ± 0.5 at. %). The following average stoichiometric formulas are TiN0.52O0.20 top and TiN0.54O0.26 bottom for top and bottom electrodes, respectively. The amount of oxygen incorporated into TiNx during PEALD because of oxygen impurities in the plasma is minor compared to that because of diffusion from SiO2 and HfO2. This asymmetry, together with results on a sample grown on a Si substrate, shows that incorporating oxygen impurity from the plasma itself is a minor part compared to diffusion from the SiO2 substrate and HfO2 dielectric during the PEALD growth. We observe the presence of TiO2 at the interface between the Hf oxide layer and the Ti nitride electrodes as well as at the SiO2 interface. EELS analysis led to a band gap ranging from 2.2 to 2.5 eV for the bottom TiNxOy and 1.7–2.2 eV for the top TiNxOy, which is in fair agreement with results obtained on the top TiNx electrode (1.6 ± 01 eV) using optical absorption spectra. Measurement of sheet resistance, resistivity and temperature coefficient of resistance by a four-point probe on the top TiNxOy electrode from 20 to 100 °C corresponds to the typical values for semiconductors