We observed two types of cracks with the direction of < 1 1 (2) over bar 0 > which are perpendicular to the < 1 (1) over bar 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 < I T 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-Al0.12Ga0.88N/GaN cladding layer. (c) 2006 Elsevier B.V. All rights reserved.