Satoshi Kamiyama

Formation and characterization of porous SiC by anodic oxidation using potassium persulfate solution

The formation process of porous SiC by anodic oxidation was investigated, aiming at the generation of pure white light with a high color rendering index (CRI) and high luminous efficiency. The efficiency of white light emission from porous SiC and its wavelength are strongly dependent on the porous structure such as the average pore size and porosity. In this study, we examined the structure and optical properties of porous SiC by adding potassium persulfate (K2S2O8) as an oxidant in HF solution to control the porosity of porous SiC formed by anodic oxidation. By increasing the amount of the oxidant, we enhanced the integrated light emission intensity of porous SiC to 81 times that of bulk SiC. Through the study of porous SiC we demonstrated that the peak wavelength of the porous SiC could be controlled from 370 to 500 nm. Porous SiC created by anodic oxidation was thus proven to have great potential for realizing high-CRI white light generation using LEDs.

Improved crystalline quality of nonpolar a-plane GaN grown on r-plane patterned sapphire substrate (Conference Presentation)

Nonpolar a-plane GaN (a-GaN) grown on r-plane sapphire substrate is one of the promising materials for eliminating an internal field in III-nitride devices. Thus, a high performance light-emitting diode can be expected by using a high crystalline quality a-GaN. In our study, we realized a high crystalline quality a-GaN by using both patterned sapphire substrate (PSS) and sputtered AlN buffer layer (sp-AlN).nThe PSS had conical patterns with a diameter of 900 nm and a height of 600 nm. The patterns placed with triangular arrangement and an interval of 1000 nm. The 30-nm-thick sp-AlN was deposited on the PSS at 300 oC. Approximately 3.5-um-thick a-GaN was grown by using metal-organic vapor phase epitaxy with optimized growth conditions. The crystalline qualities of the a-GaN were evaluated by X-ray rocking curves full width at half maximum (XRC-FWHM) for both on- and off-axis planes. Moreover, the growth behavior of a-GaN on PSS was characterized by in-situ reflectance and scanning electron microscope.nFor the on-axis GaN (11-20) plane, the XRC-FWHM in the c-axis direction of the a-GaN was 462 arcsec, whereas it was 647 arcsec in the m-axis direction. For the off-axis GaN (10-12) plane, the XRC-FWHM was 990 arcsec. These XRC-FWHMs were significantly decreased compared with that of a-GaN grown on nitridated r-plane flat sapphire. It was suggested the density of defects in a-GaN were decreased by both PSS and sp-AlN. To clarify how to defects in a-GaN decrease by using the PSS and sp-AlN the transmission electron microscope observation was performed.