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Metal organic chemical vapor deposited Gallium nitride (GaN) thin films on (111) n-Si substrate with polycrystalline β-SiC (poly-SiC), cubic β-SiC (c-SiC), and porous β-SiC (PSC) buffer layers were characterized in detail using X-ray diffraction, Fourier transform IR spectroscopy, atomic force microscope, TEM, SEM, and Raman spectrometer. The β-SiC thin film was prepared by rapid thermal chemical vapor deposition, while the PSC thin film was formed by using the electrochemical anodization on a cubic β-SiC thin film. In addition, we used the GaN thin film on different buffer layers to construct a metal-semiconductor-metal (MSM) photodiode and measured its photo/dark current ratio (PDCR) and responsivity with and without the irradiance of an UV light source for examining the ultraviolet detecting properties. Among these MSM photodiodes, the structure of GaN/PSC/n-Si achieved the highest PDCR and responsivity of 6.75 × 105 and 138 mA/W, respectively, for the lowest stress built in the GaN film.
Date of Publication: Aug. 2010