Investigations on strained AlGaN/GaN/Sapphire and GalnN multi-quantum-well surface LEDs using AlGaN/GaN bragg reflectors

Investigations were carried out on metalorganicchemical-vapor-deposition (MOCVD)-grown strained AlGaN/ GaN/sapphire structures using X-ray diffratometry. While AlGaN with lower A1N molar fraction (< 0.1) is under the in-plane compressive stress, it is under the in-plane tensile stress with high A1N molar fraction (> 0.1). Though tensile stress caused the cracks in AlGaN layer with high A1N molar fraction, we found that the cracks dramatically reduced when the GaN layer quality was not good. Using this technique, we fabricated a GalnN multi-quantum-well (MQW) surface emitting diodes were fabricated on 15 pairs of AlGaN/GaN distributed Bragg reflector (DBR) structures. The reflectivity of 15 pairs of AlGaN/GaN DBR structure has been shown as 75% at 435 nm. Considerably higher output power (1.5 times) has been observed for DBR based GalnN MQW LED when compared with non-DBR based MQW structures.