Effects of extreme dc-ageing and electron-beam irradiation in InGaN/AlGaN/GaN light-emitting diodes

Changes in the optical performances of blue light-emitting diodes based on InGaN/AlGaN/GaN heterostructures were studied after ageing stages consisting of electrical stress at a dc forward current of 100 mA and high-energy electron-beam irradiation. The structural modifications induced by ageing were investigated and a physical description of the nature of the damage was defined by means of complementary techniques such as electroluminescence, cathodoluminescence and current–voltage characterization at different temperatures. The onset of a broad optical band at about 3.08 eV and a consistent reduction of the quantum well optical efficiency revealed a substantial degradation of the heterostructure after ageing. The new band, ascribed to the formation of Mg-related complexes acting as shallow acceptors, occurred together with a dramatic change in the current–voltage curves. Its quenching after electron-beam irradiation and its recurrence after further electrical stress suggested the metastable nature of Mg-related complexes.