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A new study investigates the structural characteristics of Y2O3 films grown on oxidized Si (111) surface.

Research was conducted to examine the temperature dependence of the properties of heteroepitaxial Y2O3 films grown on Si by ion assisted evaporation. Reflection of high energy electron diffraction, X-ray scattering, Rutherford backscattering spectroscopy channeling, atomic force microscopy and transmission electron microscopy were used to investigate the film properties such as crystallinity, strain and morphology. Results indicate that many defects at the interface region were generated by interface interaction between the Si substrate and the yttrium metal.

X-ray diffraction, atomic force microscope and reflection high-energy electron diffraction were used to examine the initial and epitaxial growth stage of Y2O3/Si(100) grown by reactive ionized cluster beam deposition. Findings showed that crystalline growth of Y2O3 film depends on the state of the surface at the initial growth stage whether the Si surface was first exposed to oxygen or yttrium. The silicon layer which formed on the Si surface during the initial growth stage played a significant role in the epitaxial and preferred growth direction of the film.

Phase Change Memory (PCM) has been proposed for use as a substitute for flash memory to satisfy the huge demands for high performance and reliability that promise to come in the next generation. In spite of its high scalability, reliability, and simple structure, high writing current, e.g., RESET current, has been a significant obstacle to achieving a high density in storage applications and the low power consumption required for use in mobile applications. We report herein on an attempt to determine the level of carbon incorporated into a GeSbTe (GST) film that is needed to reduce the RESET current of PCM devices. The crystal structure of the film was transformed into an amorphous phase by carbon doping, the stability of which was enhanced with increasing carbon content. This was verified by the small grain size and large band gap that are typically associated with carbon. The increased level of C-Ge covalent bonding is responsible for these enhancements. Thus, the resistance of the carbon doped Ge2Sb2Te5 film was higher than that for an undoped GST film by a factor of 2 orders of magnitude after producing a stable face-centered cubic phase by annealing. As a consequence, the PCM devices showed a significant reduction in RESET current as low as 23% when the carbon content was increased to 11.8 at. %. This can be attributed to the elevated SET resistance, which is proportional to the dynamic resistance of the PCM device, caused by the high resistance due to a carbon doped GST film. [ABSTRACT FROM AUTHOR]

We investigated the chemical states and nature of the defect states below the conduction band edge of HfO2 films grown on GaAs (100) substrates using high-resolution x-ray photoelectron spectroscopy (HRXPS), x-ray absorption spectroscopy (XAS), and density functional theory calculations. O K1-edge absorption spectra of the HfO2/GaAs film revealed two distinct conduction band edge defect states, located at 1.6 ± 0.2 eV and 3.0 ± 0.2 eV below the conduction band edge in HfO2. The combined XAS and HRXPS results as a function of post-deposition annealing temperature indicated that the changes in defect states below the conduction band edge of HfO2 were correlated with the extent of interfacial chemical reactions between the HfO2 film and the GaAs substrate. Spectroscopic and theoretical results revealed that the two conduction band defect states are caused by (i) diffused Ga-O states, Hf3+ states, and (ii) an O divacancy related to the As-O states, respectively. [ABSTRACT FROM AUTHOR]

Zr-incorporated Gd2O3 films were grown on various substrates as a function of Zr content. The extent of interfacial reactions was found to be critically dependent on both the incorporated Zr content and the substrate type. Specifically, the silicide layer was suppressed and the Gd2O3 phase was changed to ZrO2 on a Si substrate with increasing Zr content. Crystalline Gd2Ge2O7 was grown on a Ge substrate, as the result of interfacial reactions between Gd-oxide and the Ge substrate. However, interfacial reactions were not affected by the amount of Zr incorporated. On the SiGe/Si substrate, reactions between Gd-oxide and Si could be controlled effectively by the incorporation of Zr, while the extent of reactions with Ge was significantly enhanced as the Zr content increased. The formation of an interfacial layer between the film and the SiGe substrate resulted in a textured crystalline growth. [ABSTRACT FROM AUTHOR]

Medium energy ion scattering and high-resolution transmission electron microscopy are used to investigate the depth of the interfacial reaction of Hf-silicate film. The interfacial reaction is critically affected by the film thickness and the mole fraction of HfO2 in silicate film. The interfacial compressive strain generated at the surface of the Si substrate is dependent on the film thickness during the postannealing process in film with a thickness of ∼4 nm. Finally, the phase separation phenomenon demonstrates critically different behaviors at different film thicknesses and stoichiometries because the diffusion of Si from interface to surface is dependent on these factors. Moreover, the oxidation by oxygen impurity in the inert ambient causes SiO2 top formation. [ABSTRACT FROM AUTHOR]

The phase transitions of Ge2Sb2Te5 (GST) films after bombardment with 40 keV N2+ ions were investigated. Comparing the nitrogen incorporated GST films with a pure GST film, the suppression of a crystalline grain growth was more effective in the N2+ implanted GST film than in a nitrogen codeposited GST film, i.e., x-ray diffraction data showed that the intensities of the crystalline diffraction peaks were decreased and the full widths at half maximum were broader than that of a pure GST film. This suppression of crystallization owing to the incorporation of nitrogen drastically reduced the roughness of surface morphology and decreased the electrical conductivity of the crystalline film. A near edge x-ray absorption fine structure experiment and x-ray photoemission spectroscopy data demonstrated that the suppression of crystalline grain growth is due to the formation of Ge3N4 and interstitial N2 molecules. In N2+ implanted GST films, in particular, interstitial N2 molecules played a major role in the suppression of crystallization. [ABSTRACT FROM AUTHOR]

Gd2O3 films, in which ZrO2 was incorporated, were epitaxially grown on Si(111) using an electron-beam evaporation and effusion method. The crystalline structure and morphological characteristics were investigated by various measurements. A silicide layer was locally formed during the initial growth stage due to interactions between elemental Gd and Si in the Gd2O3 film, resulting in poor interfacial characteristics and extensive destruction of the crystalline structure. However, the incorporation of ZrO2 influenced the unit-cell structure of Gd2O3, which contains oxygen vacancies that is located diagonally, enhancing the structural stability owing to the effective suppression of the interfacial layer. The effect on the initial growth stage as the result of incorporation improves the crystalline quality of the epitaxial Gd2O3 film and structural coherence between the film and substrate. [ABSTRACT FROM AUTHOR]

YSi[SUB2-x] films were grown by ion-assisted evaporation in an ultrahigh vacuum (UHV) on Si(111) through a thin SiO[SUB2] layer. The films grown on the oxidized Si were changed from a polycrystalline structure with various phases of oxides and silicides into a single-crystalline silicide structure as the annealing temperature was increased in the UHV chamber. The structural change with the annealing temperature implied that various Y[SUB2]O[SUB3] phases formed by the reaction between Y and SiO[SUB2] were decomposed and transformed into YSi[SUB2-x] under the UHV environment. Rutherford backscattering spectroscopy/channeling showed that, although the interfacial crystallinity of the film grown on the SiO[SUB2] layer was poorer quality than the film grown on a clean Si surface, a single crystalline YSi[SUB2-x] layer with high crystallinity (Χ[SUBmin] = 8%) was grown. These results showed that the difference of the thermal energy and the formation energy between the oxides of Y[SUB2]O[SUB3]-SiO[SUB2] and yttrium silicide determined the evolution of the silicide layer formation and its crystal structure. [ABSTRACT FROM AUTHOR]

We investigated the characteristics of Y[sub 2]O[sub 3] films grown on an oxidized Si(111) surface, using x-ray diffraction, Rutherford backscattering spectroscopy, and high-resolution transmission electron microscopy. The films grown on the oxidized Si show drastically improved crystallinity, compared with the film grown on clean Si surfaces: channeling minimum yield (X[sub min]) of 2.5% and full width at half maximum of rocking curve lower than 0.03°. The improvement of the crystallinity was due to the difference of the crystalline structure at the interface between the films grown on the oxidized and clean Si surfaces. Crystalline orientation of Y[sub 2]O[sub 3] islands at the interfacial region was misaligned from the normal substrate direction. The misalignment decreased with increasing the substrate temperature. In particular, the ordering of the oxygen atom in the film grown on oxidized Si was improved compared to that of the Y atom, indicating that the crystallinity of the film is dominantly determined by the arrangement of the oxygen atom in the unit cell. These characteristics of crystalline structure are influenced by the interfacial interactions among SiO[sub 2], Y, and Si. The interfacial SiO[sub 2] layer can be removed at high growth temperature above 800 °C using the reaction process; the high crystalline Y[sub 2]O[sub 3] film without any interlayer oxide can be obtained. [ABSTRACT FROM AUTHOR]

An investigation on the phase transitions of Ge2Sb2Te5 (GST) films after bombardment with 40 keV [N.sub.2.sup.+] is conducted. X-ray diffraction (XRD) results and electrical conductance measurements showed that crystallization is suppressed in the nitrogen doped GST films.

The diffusion of Ge in Ge-rich layer (GRL) and the factors affecting on it during the oxidation of strained Si1-xGex layers were examined. Strained Si1-xGex layers, having different initial Ge concentrations (x=0.15 and 0.3), were oxidized at 800 and 900 °C in a dry O2 ambient for different oxidation times. The diffusion of Ge into the underlying Si1-xGex layer having an initial constant composition and the resulting transformation to GRL were both enhanced with an increase in oxidation temperature. After complete transformation to GRL, GeO2 started to become incorporated into the resulting oxide layer. The formation of GeO2 was initiated by the Ge saturation of the GRL layer with Ge and by the differences in diffusivity of Ge atoms in Si1-xGex and Si substrate. The relaxation occurred when the Ge concentration in the GRL reached a critical value and was not affected by either oxidation time or temperature. [ABSTRACT FROM AUTHOR]