Growth and evaluation of GaN grown on patterned sapphire substrates

We report the microstructure and optical properties of gallium nitride (GaN) epilayers grown on tens shape patterned sapphire substrate (PSS) using metalorganic chemical vapor deposition (MOCVD) for various growth times. A lens shaped pattern was used to reduce the threading dislocation density and to improve optical emission efficiency. A scanning electron microscope (SEM) image shows flat and smooth surface of GaN grown on PSS at 80 min which could be achieved by lateral growth from the trench region. From the DCXRD spectra, full width at half maximun (FWHM) value was decreased with increasing growth time. FWHM of the sample grown at 80 min was 473.5 are see. This indicates there is an improvement in crystalline quality of the GaN grown on PSS as the growth time increases. From photoluminescence (PL) spectra, an increase in band edge emission intensity and a decrease in defect related yellow luminescence was observed for GaN on PSS as the growth time increased. From the PL spectra, FWHM was 82.2 meV at peak position 363.9 nm for the sample grown for 80 min. It is clearly seen that the threading dislocations can be reduced by lateral growth improving the light emission efficiency by internal light reflection on the lens surface for GaN grown on PSS.