The morphological evolution of InGaN laser diodes on laterally overgrown GaN on sapphire was investigated to understand the effect of threading dislocations (TDs) on the morphology and subsequent device performance. Screw-component TDs were found to strongly influence the surface morphology and growth mechanism of InGaN-based laser diodes. Spiral growth about mixed character TDs (Burgers vector = a + c) resulted in growth hillocks for laser structures grown directly on sapphire as well as laser structures grown on lateral epitaxially overgrown (LEO) GaN on sapphire. The dislocation distribution dominated the size of growth hillocks. Small spirals, with typical heights of 15 Angstrom and diameters of 1.5 mum, were formed on laser structures grown on sapphire due to the uniformly distributed mixed character TDs, but large spiral hillocks, with heights of 65 Angstrom and diameters up to 30 mum, developed on the LEO GaN due to the larger spacing between mixed character TDs. The spirals exhibited steps oriented in crystallographic directions, showing the six-fold symmetry of the hexagonal crystal. Spirals that formed during the growth of the active region did not diminish with subsequent high-temperature growth. Even with larger spirals, the lasers on LEO GaN exhibited reduced threshold current densities as compared to lasers grown on sapphire. (C) 2002 Elsevier Science B.V. All rights reserved.