Patterned Sapphire Substrates for III-Nitride Epitaxial Growth

Abstract

GaN-based light emitting diodes (LEDs) were epitaxially grown on patterned sapphire substrates (PSSs) to investigate the effectiveness of PSSs for improving the internal quantum efficiency (IQE) and light extraction efficiency (LEE) of the LEDs. Using X-ray diffraction (XRD) and light output measurements, it was observed that the PSSs improved the crystal quality of the LED films and enhanced the LED light intensity. Based on these experimental results, we discuss whether the enhanced light intensity can be attributed to improvements in the IQE or the LEE. The contribution of the IQE improvement to the light intensity was estimated through a comparison of the calculated light emitting area of the LED chip and the measured light output. As a result, it was revealed that the IQE improvement is not the main cause of the increase in the light intensity, indicating that the PSSs mainly improve the LEE. A comparison of the calculated number of bumps on the PSSs and the measured light output of the LEDs suggests that an increase in the number of bumps could affect the improvement in the LEE.