Fabrication and Characterization of AlGaN/GaN Double-Heterolaser Structures on Sapphire Substrates Using Single Crystalline AlN Buffer Layers

High-Al-composition AlGaN/GaN double-heterolaser structures were fabricated on sapphire substrates using single crystalline AlN buffer layers. Structures having Al0.25Ga0.75N cladding layers with a 2-µm total thickness were grown without cracks. Device performance was mainly investigated for the structure with Al0.2Ga0.8N cladding layers and a multiquantum-well-structure active layer. Optical emission was intense for devices with a multiquantum-well-structured active layer. However, no sign of stimulated emission was observed in this study.