Papers by Keyword: Buffer Layer

Abstract: The effects of annealing on epitaxial graphene on SiC substrates with various conditions are investigated. Results show that high pressure hydrogen atmosphere is more effective to decouple the epitaxial graphene from SiC substrate than that of a relative lower pressure process. Besides, the characteristic 2D-peak of graphene in Raman spectra disappeared with an annealing temperature 1000 °C, which means that the epitaxial graphene layer was decomposed in this condition. The study also shows that the decomposition of graphene can be effectively suppressed by increasing carbon vapor partial pressure through introducing ethylene during high pressure hydrogen annealing at 1000 °C. And the epitaxial graphene is successfully transferred to quasi free standing graphene by the annealing with an appropriate flow of ethylene.

Abstract: In this work the deposition of buffer layer has been studied in order to increase the quality of the epitaxial layer and improve the performance of device. The comparison between two different thicknesses of buffer layer reveals a decrease of crystallographic defects and an improvement of electrical parameters of MOSFET device as leakage current and breakdown voltage.

Abstract: We investigated the carrot-defect reduction effect by optimizing the buffer layers of 4H-Silion Carbide (SiC) epitaxial wafers. The SiC epitaxial wafer with the 0.5 μm-thick optimized condition-B buffer layer show the carrot-defect density of 0.13 cm^-2, since that with the conventional-A buffer layer were 0.68 cm^-2. Although the average bunching length with the optimized condition-B buffer layer was 7-times longer than those with the conventional condition-A buffer layer, we could reduce the bunching length by applying the optimized condition-B only to the initial 0.05 μm-thick buffer layer. Finally, with the initial 0.05 μm-thick optimized condition-B buffer layers, we could achieve the SiC epitaxial wafers with only half the carrot-defect densities of those with the conventional condition-A buffer layers, while the average bunching lengths were less than 100 μm. With this condition, we could achieve the estimated yield of 90.1% with 4 x 4 mm chips, while that with the conventional condition-A buffer layer was 81.9%.

Abstract: In this study we report the growth of graphene on different silicon carbide substrates by chemical vapor deposition (CVD) in order to understand the influence of the substrate offcut on the graphene layers. For this purpose, graphene was grown on substrates with different offcuts, under hydrogen-argon atmosphere, and analyzed using AFM, LEED and Raman spectroscopy. We discuss the morphology and strain in graphene, and finally the ideal offcut for graphene growth.

Abstract: This work reports on the CVD heteroepitaxial growth of 3C-SiC layers on diamond (100) substrates. To obtain good layer quality, the growth procedure involves a “silicidation” step consisting in depositing a silicon layer by CVD on the diamond substrate, in order to elaborate a very thin SiC buffer layer. 3C-SiC growth is then performed on this SiC seeding layer. Silicidation and growth parameters have been studied in order to improve the quality and the morphology uniformity of the heteroepitaxial layer. The study points out the role of liquid silicon during the growth process.

Abstract: The performance of phase change memory (PCM) cell, based on Ti_0.5Sb₂Te₃, was significantly improved by using a tantalum dioxide buffer layer. The presence of a buffer layer reduced the reset voltage of the PCM cell. The theoretical thermal simulation and calculation for the reset process were conducted to analyze the thermal effect of the titanium dioxide heating layer. The improved performance of the PCM cell with dioxide clad layer can be attributed to the fact that the buffer layer not only acted as heating layer but also efficiently reduced the cell dissipated power.

Abstract: The ZnO:Al (AZO) films were deposited on glass substrates with Al₂O₃ buffer layers by RF magnetron sputtering. The obtained films had the hexagonal structure and preferred orientation of (002). Compared with AZO film without buffer layer, the grain size of the film with buffer layer was increased and the conductive property was increased greatly. the grain size of AZO films reached 27.9nm for those with buffer layers. The optical property of AZO films was decreased by the buffer layers. The resistivity of AZO films with Al₂O₃ buffer layer was about 6.6×10^-3 Ω·cm and the average transmittance was over 80% in the range of 450~900nm.

Abstract: Westudy the structural characteristic of carbon based thin filmprepared by DC unbalanced magnetron sputtering technique on different buffer layer such as γ-Al₂O₃, SnO₂, and Cu. Sputtering parameters of carbon thin film were maintained identical for each buffer layer. Fe-doped carbon pellet and Argon gas have been used as sputtering target and to generate the sputtering plasma, respectively. The roles of buffer layer for the quality of carbon-based thin film have been investigated by X-ray diffraction and Raman spectroscopy analysis. Raman spectra indicatethe formation of agoodquality carbon thin film with crystal-like structure on γ-Al₂O₃and Cu buffer layer, in contrast to the SnO₂buffer layer case. Furthermore Raman spectra confirm thehoneycomb structure with fewer defects in γ-Al₂O₃ indicating that it is more suitable buffer layer than the other. We argue that γ-Al₂O₃ buffer layerprovide a good nucleation site and promote a better atomic arrangement for carbon atoms to form a few layergraphene-like structure. The atomic geometry of γ-Al₂O₃ supports the hexagonal atomic configurationfor carbon atom inthe formation of a few layers graphene. This study mightgive a new approach for the carbon based deposition towards the devices application.

Abstract: The TiN ceramic films were deposited on Si (100) substrates with Al and Ti buffer layers by direct current reactive magnetron sputtering in the mixture gas atmosphere of argon and nitrogen. X-ray diffraction (XRD), Raman spectroscopy, scanning electronic microscope (SEM), nanohardness test and ultra violet-visible-near infrared (UV-VIS-NIR) spectrophotometer were employed to analyze the structure, mechanics and optical characteristics of the TiN films respectively. Analyses of XRD and Raman showed that all the TiN films deposited on Al and Ti buffer layers with TiN (111)-preferred orientations had polycrystalline structures, and the TiN film deposited on Ti buffer layer had a better crystallinity, smaller surface roughness, higher hardness and larger elastic modulus than those of the TiN film deposited on Al buffer layer. Moreover, the reflectivity of the Ti/TiN film became higher than Al/TiN film above λ=645 nm. At λ=1200 nm, the Ti/TiN film showed the maximum reflectivity of 81.8%. These conclusions also showed that the metal multilayer TiN films have important application and research prospect in terms of solar control coatings or resistance to high temperature in building coating material.

Abstract: Due to its high in-field superconducting performance, high irreversible magnetic field, low AC loss and high transition temperature, YBa₂Cu₃O_7-x (YBCO) has been taken as a hot research object. Well-oriented La_0.4Sr_0.6TiO₃(LSTO) thin films were prepared on the biaxially textured Ni-W alloy substrates by metal-organic deposition (MOD) method which could used for YBCO coated conductor. The homogeneous and stable precursor solution was prepared by Y, Ba and Cu acetates and deposited on LSTO/Ni-W composite structure by spin-coating method. YBCO films were obtained after heat treatment. Effect of thermal decomposition time on YBCO films was discussed,and the results showed that the proper time of organic decomposition was 3h at 400°C.