Extensive investigation of the electrical and optical characteristics of Gate Injection Transistors based on GaN

Despite the recent progresses in the technology of GaN-based laser diodes (LDs), there is a number of physical mechanisms that limit the reliability of these devices. Both catastrophic and gradual degradation can occur during the operation of a GaN-based LD. Catastrophic degradation is usually ascribed to the damage of the facets or to dislocation-related issues. On the other hand, the physical mechanisms responsible for gradual degradation have not been univocally identified, and this is generating an important discussion in the GaN-laser community. Different mechanisms have been proposed as responsible for the gradual degradation of laser diodes, including: (i) the increase in the non-radiative recombination rate in the active region of the devices; (ii) the increase in the leakage current components; (iii) the worsening of the current confinement under the ridge. With this paper we present a detailed analysis of the degradation of GaN-based LDs, carried out by electrical and optical characterization techniques: results give a strong indication that the degradation of LDs is related to an increase in the non-radiative recombination, rather than to the worsening of current confinement. The study was carried out both on laser diodes and on LED-like devices having the same epitaxial structure of the LDs, but with no ridge and facets. LDs and LED-like samples were stressed at similar current density and temperature levels (J>4 kA/cm2), in order to achieve a consistent comparison between the results obtained on the two kinds of devices