Growth and strain characterization of high quality GaN crystal by HVPE

Freestanding GaN crystals were fabricated by hydride vapor phase epitaxy using a random-islands facet-initiated epitaxial overgrowth technique. In this method, small micrometer sized GaN islands were firstly deposited on a TiC buffer layer on a sapphire substrate. Successive three-dimensional growth of GaN was controlled to a thickness of a few hundred micrometers on the buffer layer. Finally, a thick GaN layer was grown and high quality freestanding GaN crystals (dislocation density: <3×10⁶ cm⁻², radius of curvature: >5 m) were obtained by self-separation from the sapphire substrate. It was found that the dislocation density was drastically reduced in the initial growth stage of this method by the appearance of sidewall facets. Depth profiles of the residual strain in the freestanding GaN substrates have been successfully measured by a novel method employing cross-sectional micro-reflectance spectroscopy. It was found that the intrinsic strain, the driving force of wafer bending, can be greatly reduced by the introduction of three-dimensional growth in the initial growth stage.

Source: Journal of Crystal Growth

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Residual strain in annealed GaAs single-crystal wafers as determined by scanning infrared polariscopy, X-ray diffraction and topography

We have compared the strain data in GaAs wafers, as-grown as well as annealed, determined by means of the scanning infrared polariscope (SIRP) with data of high-resolution X-ray diffraction (HRXD) and qualitative results of a synchrotron based, single-crystal X-ray transmission topography (SXRTT) study. The in-plane strain component |ε_r−ε_t| measured by SIRP throughout the wafer thickness was about 10⁻⁵, while it derived from the single components ε_xx,ε_yy , and ε_xy determined by HRXD at a penetrated layer close to the surface was above 10−4. Consequently, we assume that a strong strain gradient exists between the surface and the bulk.

Source:Journal of Crystal Growth

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Plastically deformed Ge-crystal wafers as elements for neutron focusing monochromator

Plastically deformed Ge-crystal wafers that have the cylindrical shape with a large curvature were characterized by neutron diffraction. The box-type rocking curve of Bragg reflection with the angular width of Γbox≃2° in FWHM, which is observable in the monochromatic neutron diffraction, results in an enhancement in the angle-integrated intensity (Iθ). Besides, Iθ efficiently increases by stacking such Ge wafers. In the course of white neutron diffraction, the reflected-beam width near the focus point becomes sharper than the initial beam width. Further, the dependence of the horizontal beam width on the distance between the sample and detector is quantitatively explained by taking account of the large Γbox, the small mosaic spread of η≃0.1°, and the thickness of the wafers. On the basis of these characterizations, use of plastically deformed Ge wafers as elements for high-luminance neutron monochromator is proposed.

Source：sciencedirect

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Growth of thin SiC films on Si single crystal wafers with a microwave excited plasma of methane gas

We have studied the growth and properties of SiC films on Si wafers, under ultrahigh vacuum background conditions, using a remote-, microwave excited, methane plasma as a source of active carbon and hydrogen, while the Si substrates were held at a temperature of near 700 °C. The reaction is diffusional and should thus be self-limiting, but it actually reaches up to 20–25 nm thickness due to direct transport of Si from the substrate to the top surface through initially open defects in the growing film. These defects gradually fill up during the growth, and the resulting films have a relatively low density of these, and are otherwise very uniform and polycrystalline. They are characterized with scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and hardness measurements.

Highlights

• Self-limiting SiC film growth on Si

• Methane plasma

• Films of very high quality

Source：Thin Solid Films

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Nondestructive three-dimensional observation of defects in semi-insulating 6H-SiC single-crystal wafers using a scanning laser microscope (SLM) and infrared light-scattering tomography (IR-LST)

Peripheral and central areas of a semi-insulating 6H-SiC single-crystal wafer were examined using a scanning laser microscope (SLM) and infrared light-scattering tomography (IR-LST). The form and density of the defects in each area were observed by SLM. We reconstructed three-dimensional (3D) IR-LST images of scatterers by stacking 2D layer-by-layer IR-LST images on different planes. Using these 3D IR-LST images, variations in the defect distribution with depth were observed for the first time. To study the defect distribution and defect form in detail, we observed the defect configuration in the same volume as for 3D IR-LST images by magnified SLM and merged the images from the two techniques. Information on defects obtained using this approach will be very important in the development of high-quality semi-insulating silicon carbide (SiC) substrates.

Source：Journal of Crystal Growth

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