Growth and characteristics of InGaN/GaN films grown on hemispherical patterned sapphire by using MOCVD

To enhance light extraction efficiency, high-quality InGaN/GaN film was grown on hemispherical patterned sapphire (HPS) by using metal organic chemical vapor deposition. A detailed analysis of X-ray diffraction patterns resulted in a shorter lattice constant c of 5.1877 angstrom for the GaN thin films grown on HPS substrate, compared to 5.1913 angstrom for the samples grown on conventional sapphire substrate (CSS). The surface pattern of the HPS substrate seems to be more helpful for the accommodative relaxation of compressive strain related to the lattice mismatch between GaN and sapphire substrate. The luminous intensity of a white flash-light-emitting diode (LED) grown on HPS was estimated to be 5.8 cd at a forward current of 150 mA, which is improved by 20 % compared to that of a LED grown on CSS substrate. It was also found that the maximum saturation current was increased from 400 mA for LEDs grown on conventional sapphire to 550 mA for LEDs grown on HPS. The improvement of luminous intensity was explained by considering not only an increase of the extraction efficiency via the suppressed total internal reflection at the corrugated interface but also a decrease of dislocation density.