State of the art in the reliability of GaN-based laser diodes

Over the last few years important efforts have been done with the aim of improving the performance of InGaN-based laser diodes (LDs): as a result, blue-violet laser diodes with power levels in excess of 1-3 W are now commercially available, and record-wavelengths in excess of 530 nm have been recently demonstrated for green LDs. Despite the excellent performance of InGaN-based laser diodes, their reliability is still limited by a number of physical mechanisms, including (i) the generation of non-radiative centers within the active region; (ii) the degradation of the facets; (iii) the diffusion of point defects; (iv) dislocation-related issues; (v) the worsening of current confinement under the ridge. The aim of this paper is to give an overview on the physical mechanisms that are responsible for the long-term degradation of violet GaN-based LDs: we will compare the different theories invoked to explain the degradation of LDs, by describing both literature data and recent results obtained in our laboratories. We will further show that optical analysis, Capacitance-Voltage profiling and DLTS investigation represent powerful tools for the investigation of the degradation of InGaN-based heterostructure devices