Growth of crack-free thick AlGaN layer and its application to GaN-based laser diode

In the field of group-III nitrides, hetero-epitaxial growth has been one of the most important key technologies. A thick layer of AlGaN alloy with hig her AlN molar fraction is difficult to grow on sapphire substrate, because the alloy layer is easily cracked. It is thought that one cause of generati ng cracks is a large lattice mismatch between an AlGaN and a GaN, when AlGa N is grown on the underlying GaN layer. We have achieved crack-free Al0.07G a0.93N layer with the thickness of more than 1 mum using underlying Al0.05G a0.95N layer The underlying Al0.05Ga0.95N layer was grown directly on sapph ire by using the low-temperature-deposited buffer layer (LT-buffer layer). Since a lattice mismatch between the underlying Al0.05Ga0.95N layer and upp er Al0.07Ga0.93N layer is relatively small, the generation of cracks is tho ught to be suppressed. This technology is applied to a GaN-based laser diod e structure, in which thick n-Al0.07Ga0.93N cladding layer grown on the Al0 .05Ga0.95N layer, improves optical confinement and single-robe far field pa ttern in vertical direction.