Michiya Odawara

Organometallic chemical vapor deposition growth of heterostructure of wide band gap and transparent boron phosphide on silicon

A boron phosphide (BP) layer was grown on the (111) Si substrate by atmospheric pressure organometallic chemical vapor deposition (MOCVD) using triethylboran ((C2H5)3B) and phosphine (PH3) sources. By transmission electron diffraction analysis, the transparent BP layer was found to grow on (111) Si with the following orientation: (111), -Si//(111), -BP. The MOCVD-grown BP layers exhibited transparency under fluorescent light illumination. Reflected light color was observed to vary depending on the thickness of the BP layer. The refractive index (n) of the heteroepitaxial (111) BP layer was revealed to decrease from 3.16 at a wavelength (λ) of 350 nm to 2.77 at λ of 750 nm. The extinction coefficient (k) corresponding to n at λ of 350 nm was 0.19. Refractive index (n) and k at λ of 350 nm gave 9.95 as the real part of the complex dielectric constant of the MOCVD-grown BP layer. The optical evaluation indicated that BP is applicable as a transparent III-V semiconductor layer for forming heteroepitaxial structures with Si.

Step-Bunching Free and 30 μm-Thick SiC Epitaxial Layer Growth on 150 mm SiC Substrate

The production of 150 mm-diameter SiC epi-wafers is the key to the spread of SiC power devices. Besides, step-bunching free surface leads to high-performance devices. We have developed the production technology of the epitaxial growth with smooth surface morphology for 4º off Si-face 4H-SiC epitaxial layers on 150 mm diameter substrates. The various area observations of the surface by optical surface analyzer, confocal microscope and atomic force microscope revealed that there was no conventional step-bunching in whole wafer surface. While creating step-bunching free surface is more difficult for thicker epilayer growth, we have achieved step-bunching free surface for 30-μm thick epilayer on a 150 mm diameter substrate. The typical values of thickness uniformity of the 30μm-thick epilayer are 0.5% (σ/mean) and 1.7% (range/mean). A few interfacial dislocations (IDs) were detected for the 150 mm-diameter epi-wafer by reflection X-ray topography. We have succeeded in removal of IDs by the optimized growth condition.

4H-SiC Epitaxial Growth on C-Face 150 mm SiC Substrate

The production of 150 mm-diameter SiC epitaxial wafers is the key to the spread of SiC power devices. We have developed production technology of the epitaxial growth for 4° off Carbon face (C-face) 4H-SiC epitaxial layers on 150 mm diameter substrates. Several growth parameters and hardware were optimized to obtain high uniformity wafers. We have succeeded in fabricating high quality C-face wafers with smooth surface and high uniformity.

Characterization of (4,4)- and (5,3)-Type Stacking-Faults in 4deg.-Off 4H-SiC Epitaxial Wafers by Synchrotron X-Ray Topography and by Photo-Luminescence Spectroscopy

Experimentally,the grazing-incident X-ray topography at different diffraction conditions, and room temperature photo-luminescence spectroscopy, various different types of stacking-faults in epitaxial films on 4-degrees-off 4H-SiC wafers were identified precisely without wafer cutting. Their types and the numbers were investigated statistically. It became clear that (4,4) type stacking-faults were the most common ones and two different types were identified. Still 34% of the stacking-faults were unknown types in the present investigation.Several different kinds of stacking-faults formed on the surface of 4-degrees-off 4H-SiC epitaxial wafers were investigated. Their types could be identified and type distribution in a wafer could be obtained using X-ray topography and room temperature Photo-Luminescence without wafer cutting. Type determination of 8H(4,4)- stacking fault ; with or without strain field, could also be decideddemonstrated using this method.

Short-Length Step Morphology on 4° Off Si-Face Epitaxial Surface Grown on 4H-SiC Substrate

We developed a production technology for epitaxial growth with a smooth surface morphology for 4º off Si-face 4H-SiC epitaxial layers on 100 mm-diameter substrates. High-contrast topography images by optical surface analyzer revealed that a step bunching free surface was obtained throughout the whole area of the wafer surface. However, short-length steps still remained locally on the epitaxial surfaces. Using photoluminescence imaging, it was clarified that the short-length steps were morphological in nature and did not contain stacking faults. The short-length steps were generated by step-flow growth pinning caused by the shallow pits of threading screw dislocations revealed by molten KOH etching.

Defects Grouping and Characterizations of PL-Imaging Methods for 4H-SiC Epitaxial Layers

4H-SiC epitaxial wafers were prepared for the investigation of epitaxial stacking faults (SFs), for the purpose of classification and add to the epitaxial specification by PL-imaging analysis. Black colored SFs detected in PL colored images were focused, and investigated. Black SFs in the PL images were classified for two species, ones were correspond to the triangular defects, and the others were similar to the known SFs. Triangular defects were the killer defects for the I-V properties and the other black defects were not affected the I-V properties. Most of PL spectrums of triangular defects had the 538nm peak, and showed the 3C properties. Black defects undetectable as the surface defects (SDs) had 460, 480nm peak, differed from the reported typical 1-4SSFs spectrum. It seemed that these defects differed from the thickness of stacking layer and PL peak, whether the defects led to detectable/undetectable as the SDs. Thick stacking layers generated the triangular defects, and thin ones generated the PL-black defects undetectable as the surface analysis. Consequently, the black defects undetectable as the surface analysis (detected only for the PL-imaging analysis) has no use for add to the specification at the moment.