Light emission in GaN HEMTs: a powerful characterization and reliability tool

GaN-based high electron mobility transistors (HEMTs) are nowadays of major interest due to their high frequency and high-power performances. Although power densities up to 32 W/mm have been recently demonstrated, reliability is still one of the issue that has to be addressed in order to move toward commercially available devices. Sub-micrometer gate-length GaN HEMTs, which typically operate at very high drain-source voltages, VDS, may be prone to the same degradation mechanisms. Experimental methods capable of characterizing hot carrier effects should therefore be developed, in order to compare different device structures, or quantitatively assess lifetime accelerating factors corresponding to different bias conditions. In this paper we propose a methodology for the characterization of hot carrier effects and their dependence on bias conditions based on electro-luminescence (EL) measurements. It will also been shown that EL measurements can be used as a powerful characterization failure analysis tool, in order to study degradation and breakdown mechanisms in GaN HEMTs.