Papers by Keyword: C/Si Ratio

Abstract: In this study, we struck a balance between specular surface morphology and polytype homogeneity on an epitaxial layer grown on 4H-SiC Si-face substrate with off angle less than 1degree by controlling the C/Si ratio with the SiH₄ flow rate. Schottky barrier diodes fabricated on a grown epitaxial layer exhibited a blocking of voltage over 1000 V and an n value of less than 1.1 with a high yield of more than 80%. A substrate with a low off angle was found to have an advantage as regareds the stress that generates the interfacial dislocations at the epitaxial layer/substrate interface during the epitaxial growth process.

Abstract: 4H-SiC epilayers are homoepitaxially grown on 4H-SiC substrates with different C/Si-ratios and different growth rates by the chemical vapour deposition method. DLTS investigations are applied in order to trace energetically deep states of electrically active point defects and extended defects, which may act as the source for the degradation of electronic devices. In addition, the dependence of the DLTS signal heights on the filling pulse length is studied.

Abstract: Nitrogen doped 4H-SiC epitaxial layers grown by hot-wall chemical vapor deposition were investigated by deep level transient spectroscopy after irradiation with 6 MeV electrons or 1.6 MeV protons. The influence of silane and propane flows used during the epilayers growth on the behaviour of radiation induced EH6,7 levels is studied. Samples grown under different conditions were investigated: 1 sample grown in steps of different C/Si ratio obtained by changing the propane flow only; 1 sample grown in steps of different C/Si ratio obtained by changing the silane flow only; 2 samples grown with a C/Si ratio of 1.5 but with different flows of propane and silane. These investigations revealed that the low thermal stability of EH6,7 (the defects anneal out at temperatures as low as 750K) is due to the magnitude of silane flow used during the growth irrespective of the C/Si ratio. A possible structure of the EH6,7 defect is discussed.

Abstract: A comparative study of the morphology of 3C-SiC films prepared with different C:Si ratios is presented. The silane precursor controls the growth rate at all values of C:Si ratio but combined of observations using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) indicates that the C:Si ratio is critical in determining the grain size and at values of C:Si close to 1 texturing and faceting become evident. Makyoh Topography reveals various surface defects, a slight mesoscale roughness and bending of the epiwafers.

Abstract: The novel technique microwave detected photo induced current transient spectroscopy (MD-PICTS) was applied to semi-insulating 6H-SiC in order to investigate the properties of inherent defect levels. Defect spectra can be obtained in the similar way to conventional PICTS and DLTS. However, there is no need for contacting the samples, which allows for non-destructive and spatially resolved electrical characterization. This work is focused on the investigation of semi-insulating 6H-SiC grown under different C/Si-ratios. In the corresponding MD-PICTS spectra several shallow defect levels appear in the low temperature range. However the peak assignment needs further investigation. Additionally different trap reemission dynamics are obtained for higher temperatures, which are supposed to be due to different compensation effects.

Abstract: Modeling and simulation of the SiC growth processes, Physical Vapor Transport (PVT), Chemical Vapor Deposition (CVD), are sufficiently mature to help building new process equipment or up-scaling old ones. It is possible (i) to simulate accurately temperature and deposition distributions, as well as doping (ii) to quantify the limiting phenomena, (iii) to understand the important role of different precursors in CVD and hydrogen additions in PVT. The first conclusion of this paper is the importance of the "effective" C/Si ratio during CVD epitaxy in hot-wall reactors and its capability to explain the doping concentrations. The second conclusion is the influence of the C/Si ratio in alternative bulk growth technique involving gas additions.

Abstract: Nitrogen doped 4H-SiC epitaxial layers grown by hot-wall chemical vapor deposition were investigated by Deep Level Transient Spectroscopy after irradiation with 6 MeV electrons at room temperature. This study is focusing on the influence of nitrogen doping and C/Si ratio on the behaviour of the Z1,2 and EH6,7 levels which occur in already as-grown material but are substantially enhanced by electron and ion irradiation. It was found that both the Z1,2 and EH6,7 concentrations increase with both the nitrogen doping and the C/Si ratio. However, while the Z1,2 concentration increases during post-irradiation thermal treatment the opposite holds for the EH6,7 level especially in silicon rich samples. On the basis of these results, the influence of carbon and nitrogen on the formation of the Z1,2 complex is reconfirmed and a possible identity of the EH6,7 defect is discussed.

Abstract: Epitaxial layers have been grown on the (0001) C-face of 2- and 3-inch 4H-SiC wafers. Growth conditions like temperature, pressure, and C/Si ratio have been varied. In both systems smooth surface morphologies could be obtained. The main challenge of epitaxial growth on the Cface of 4H-SiC for electronic device applications seems to be the control of low doping concentration. High temperature and low pressure are the key parameters to reduce the nitrogen incorporation. The hot-wall CVD system used for these experiments allowed the application of higher temperatures and lower pressures than the cold-wall equipment. The lowest doping concentration of 2.5x1015 cm-3 has been achieved by hot-wall epitaxy using a temperature of 1625 °C, a system pressure of 50 hPa, a C/Si ratio of 1.4, and a growth rate of 6.5 2mh-1. Good doping homogeneity on 2-inch and 3-inch wafers could be achieved. For a doping level of ND-NA= 3×1015 cm-3 sigma is about 15%.

Abstract: The initial homoepitaxial growth behavior on nearly on-axis 4H-SiC substrates was investigated. We have observed circular etch pits on the surface of on-axis substrate in the presence of source gases. However, there were no circular etch pits on the surface of off-axis substrates. In addition, the surface etched by H2 gas did not show circular etch pits even on nearly on-axis substrates. The shape of the circular etch pits was similar to spiral one. The initial growth behavior of epilayers was also investigated with various C/Si ratios of source gases (0.6

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