Degradation of GaN-based high-power lasers and recent advancements

The degradation mechanism of blue-violet laser diodes (BV-LDs) fabricated on epitaxial lateral overgrowth (ELO) GaN on sapphire substrates is investigated and the characteristics of recent BV-LDs fabricated on GaN substrates are reported. The lifetime of lasers on ELO-GaN/sapphire is shown to be strongly dependent on the dislocation density of the basal GaN layer, with the degradation rate being roughly proportional to the square root of the operating time. Electron microscopy confirms that the degradation is not due to the multiplication of threading dislocation but rather the diffusion of defects toward dislocations in the active layer, which results in an increase in the capture cross-section for non-radiative recombination centers. BV-LDs on GaN substrates are demonstrated to have a lifetime of over 2000 h under 160 mW pulsed operation at 80 °C and to achieve a high critical power density at catastrophic optical damage (COD) of 40.8 MWcm-2.