Papers by Author: Hiroshi Harima

Abstract: The structure of ZnO thin films grown in room temperature by reactive DC sputter technique on polyethylene terephthalate film were evaluated by SEM and TEM. The quality of ZnO thin films grown in room temperature were observed to vary widely. ZnO crystals grow without uniform orientation in early stage of growth, and then ZnO crystallinity improves as the ZnO thin films grow up. And ZnO crystallinity is influenced by roughened surface of PET film.

Abstract: We report microscopic Raman scattering studies of epitaxial graphene grown on SiC substrates using a deep-ultraviolet (UV) laser excitation at 266 nm to elucidate the interaction between the graphene layer and the substrate. The samples were grown on the Si-face of vicinal 6H-SiC (0001) substrates by sublimation of Si from SiC. The G band of the epitaxial graphene layer was clearly observed without any data manipulation. Increasing the number of graphene layers, the peak frequency of the G-band decreases linearly, while the peak width and the intensity increase. The G-band frequency of the graphene layers on SiC is higher than those of exfoliated graphene, which has been ascribed to compression from the substrate.

Abstract: We have studied InGaN single-quantum-well (SQW) films using atomic force microscopy (AFM) and cathodoluminescence (CL) spectroscopy. It has been found that a screw dislocations (SDs) distribution in the height image by AFM is well correlated with images of the CL spectra at about 440nm assigned to the spontaneous emission from the InGaN SQW. These results at least mean an existence of non-radiative recombination centers within the InGaN SQW films. It has been also found that the average period of the peak-intensity and the FWHM change is smaller than that of the peak-wavelength change assigned to InN mole fluctuations. These results suggest that the exciton diffusion length of the spontaneous emission at about 440nm is not larger than the average period of InN mole fluctuations in the InGaN SQW.

Abstract: We have measured cathodoluminescence (CL) spectra in the vicinity of V-defects in InGaN single-quantum-well(SQW) films at nanometer level, using newly developed CL apparatus (SE-SEM-CL). From spectroscopic CL measurement, it has been found that the spectra change dramatically in the vicinity of V-defects in the region of £50nm. The SE-SEM-CL has a potential to detect the CL spectral variation at spatial resolution with £50nm.

Abstract: We have presented a combined method of microscopic measurements between Raman scattering and polarizing optical microscope to characterize inhomogeneous residual stress distributions around dislocations in 4H- and 6H-SiC wafers. First, stressed portions were found in wafers by an optical polarizing microscope under a crossed Nicole arrangement. Then, the portions were examined by Raman-imaging technique for lateral variations of phonon spectra. The residual stresses were quantified from the phonon-peak frequency shift using a known frequency-shift rate for 6H-SiC. Characterization to the depth direction was also conducted by surface etching with molten KOH. The stresses typically amounted to the order of 100 MPa. In a 4H-SiC homoepitaxial wafer sample, we observed threading dislocations transferred from the substrate to the epitaxial layer, and found that larger stress fields existed in the epitaxial layer than the substrate. We also observed stress distributions around compressively stressed sub-grain boundaries.