In this paper we will discuss the application of almost dislocation-free, high-pressure grown gallium nitride bulk crystals as a substrate for the epitaxy of GaN/InGaN/AlGaN laser diode structures. We show that these laser diodes may have very low dislocation densities (even down to 8 x 10(4) cm(-2)). These dislocations appear during the growth of the laser structure as a result of the combined effect of strain and perturbation of the atomic step flow. We show also that the lifetime of these devices seems to be dependent on operating current via the increasing junction temperature. (c) 2008 Elsevier B.V. All rights reserved.