Micro-crack-free high power blue-violet GaN-based laser diodes grown on maskless epitaxial lateral overgrown GaN/sapphire

Abstract

We observed two types of cracks with the direction of 〈1 1 2¯ 0〉 which are perpendicular to the 〈1 1¯ 0 0〉 stripe direction of seed GaN in the GaN-based laser diodes (LDs) structures grown on maskless ELO-GaN/sapphire substrates. It implies that both cracks must be generated by the anisotropic tensile stress to the direction of 〈1 1¯ 0 0〉 originated from the lattice and thermal mismatches between AlGaN cladding layer and maskless ELO-GaN grown on the stripe seed GaN/sapphire. These cracks were easily generated by increasing the tensile strain in the LDs structures with n-AlGaN cladding layer more than about 10% Al composition in our experiment. However, in order to reduce the threshold current, it is necessary to improve the optical confinement factor (OCF) of GaN-based LDs structure by increasing the Al composition of AlGaN cladding layer. Therefore, we could achieve that the threshold current of blue-violet GaN-based LDs can reduce to 30 mA by increasing the OCF as well as suppressing the generation of crack in the LD epilayer with the n-Al 0.12Ga 0.88N/GaN cladding layer.