Papers by Keyword: Epitaxial Growth

Abstract: Among the types of dislocation seen in homo-epilayers of SiC grown upon 4H-SiC wafers with an 8° surface offcut are basal plane dislocations propagated into the epilayer at an 8° inclination, and threading edge dislocations. These types may be imaged by monochromatic synchrotron x-ray topography in the grazing-incidence reflection geometry using the 11 2 8 reflection. Equations needed to apply the ray-tracing method of computer simulating x-ray topographic defect images in this experimental geometry were derived and used to simulate images of the threading edge dislocations. Simulations of the threading edge dislocations showed 4 μm wide white ovals with narrow arcs of dark contrast at their ends, inclined relative to the g-vector of the topograph according to the sign of their Burgers vector. These resembled the experimental topographs, inasmuch as was possible at the maximum resolution of x-ray topographs.

Abstract: Thick epitaxial layers of 4H-SiC both n- and p-type were grown using horizontal Hot- Wall CVD (HWCVD). No large difference in the carrier lifetime was observed for the layers grown on n- and p-type substrates. The carrier lifetime usually increases with the increasing thickness of the epilayer. To investigate if the growth conditions and material properties are changing during the longer growth time a sample was prepared with uniformly varying epilayer thickness from 20μm on one side to 110μm on other side. Results of optical and electrical measurements, the variation in background impurities and other deep levels are discussed. Furthermore, the properties of thick layers grown on on-axis substrates are presented.

Abstract: In this work, the mechanism of the epitaxial growth of 4H SiC using CH3Cl as the carbon source gas was investigated. The experiments were conducted with a H2 carrier gas flow rate reduced in comparison to the standard conditions used for device-quality, full-wafer C3H8 growth. Low-H2 conditions have been found favorable for investigating the differences between the two gas systems. A non-linear trend of the growth rate dependence on CH3Cl flow was observed. This dependence was quantitatively different for C3H8 growth, which serves as an indication of different kinetics of CH3Cl and C3H8 precursor decomposition, as well as differences in Si droplet formation and dissociation. The maximum growth rate that we were able to achieve was by a factor of two higher for the CH3Cl precursor than for the C3H8 precursor at the same temperature and flow conditions. The growth on lower off-axis angle substrates produced surface morphology degradation similar for both CH3Cl and C3H8 precursor systems.

Abstract: The advantages of the CH3Cl carbon precursor were investigated in order to achieve good-quality homoepitaxial layers of the 4H-SiC polytype at temperatures lower than what was considered practical (or even possible) with C3H8-based growth. It was observed that the process window for good epilayer morphology becomes narrower when the growth temperature is decreased. Successful growth experiments have been conducted in this work down to a temperature of 1290-13000C, with the growth rate in excess of 2 +m/hr and a mirror-like defect-free epilayer surface morphology. Growth on a 2” substrate produced promising growth rate homogeneity. The dependence of the growth rate on SiH4 flow followed a clear exponential dependence. This trend is tentatively attributed to Si vapor condensation. Photoluminescence results suggest that the crystalline quality of the epilayers grown at 13000C is comparable to that of 17000C growth.

Abstract: 4H-SiC epitaxial layers on Carbon-face (C-face) substrates were grown by a low-pressure hot-wall type chemical vapor deposition system. The C-face substrates were prepared by fine mechanical polishing using diamond abrasives with the grit size of 0.25 %m and in-situ HCl etching at 1400°C, which produced surface roughness of 0.27 nm. The use of the smooth substrates made it possible to decrease the substrate temperature and specular surface morphologies were realized at C/Si ratios of 1.5 or less both for a substrate temperature of 1550°C and for that of 1500°C. Surface roughness of 0.26 nm and the residual donor concentration of 6.7×1014 cm-3 were obtained for a C-face epitaxial layer grown at a C/Si ratio of 1.5 and at a substrate temperature of 1550°C. Schottky barrier diodes were fabricated on a non-doped C-face epitaxial layer grown at 1500°C and it was verified that a high quality metal-semiconductor interface was formed on the epitaxial layer.

Abstract: Bulk n+-4H-SiC wafers (n=1-2×1019 cm-3) containing annealing-induced stacking faults were examined by Raman scattering. The coupled plasmon-LO mode was observed to shift in a manner consistent with 1018 cm-3 doping in the 4H-SiC. Numerical simulations were performed using a self-consistent Poisson-Schrödinger solver and agree well with the experimental observations of carrier transfer from the 4H-SiC into the 3C-SiC stacking faults. The Raman data also shows that the 3C stacking faults induce a tensile strain on the surrounding 4H-SiC regions.

Abstract: The liquid film re-growth behaviour resulting from pulsed laser surface melting (LSM) has been investigated for typical 2xxx, and 7xxx aerospace alloys, both on parent plate and friction stir welded (FSW) joints. In Zr free alloys, as a result of the high growth rate and steep thermal gradient, the melted layer re-grew with a stable front, epitaxially, from the parent subsurface grains. This caused a thin coarse grained solidified layer to form over the parent material, thermomechanically affected zone (TMAZ) and heat affected zone (HAZ), and fine columnar grains to develop over the FSW nugget zone of the same order in width as the nugget grain size. In the case of the Zr containing alloys, a very fine columnar grain structure was found over the entire surface, independent of the subsurface grain structure. This has been shown to occur by growth selection from a band of nanoscale Al grains epitaxially nucleated on Al3Zr dispersoids, at the melt solid interface, that had not fully dissolved in the melt.

Abstract: KNbO3 thin films were grown on (100) and (110) SrTiO3 substrates by liquid phase epitaxy (LPE) technique. The film orientation and surface morphology were characterized by XRD and AFM, respectively. The limited phase diagram of K2O-Nb2O5-V2O5 system was prepared by DTA measurement to investigate the effect of V2O5 flux on the LPE growth of KNbO3 film. The use of V2O5 flux enhanced a film growth rate at lower growth temperature.

Abstract: YBa2Cu3O7-δ (YBCO) films were deposited on (100), (110) and (111) oriented silver single crystals and {100}<100>, {110}<211> , {110}<100>+{110}<011>， {110}<011> and {012}<100> textured Ag substrates using pulsed laser deposition. The relationship between the epitaxial growth YBCO film and silver substrate has been determined. It is shown that among polycrystalline Ag substrates, {110}<011> textured tape is suitable for the deposition of YBCO thin films having strong texture.

Abstract: The effects of the Si/H2 ratio on the growth of the epitaxial layer and on the epitaxial defects was studied in detail. A large increase of the growth rate has been observed with the increase of the silicon flux in the CVD reactor. Close to a Si/H2 ratio of 0.05 % silicon nucleation in the gas phase occurs producing a great amount of silicon particles that precipitate on the wafers. The epitaxial layers grown with a Si/H2 ratio of 0.03% show a low defect density and a low leakage current of the Schottky diodes realized on these wafers. For these diodes the DLTS spectra show thepresence of several peaks at 0.14, 0.75, 1.36 and 1.43 eV. For epitaxial layers grown with higher values of the Si/H2 ratio and then with an higher growth rate, the leakage current of the Schottky diodes increases considerably.