The role of Mg complexes in the degradation of InGaN-based LEDs

The electrical and optical properties of commercial blue InGaN-based LEDs after room temperature aging tests at DC-forward currents from 50 to 100 mA are studied by Current–Voltage, Capacitance–Voltage, Electroluminescence and Cathodoluminescence techniques. An increase of the reverse and low-bias forward currents, of the parasitic series resistance and a substantial optical intensity reduction are observed in all the devices investigated with or without heat sink. In addition, only in devices aged at 100 mA without heat sink, the onset of a broad optical band peaked at about 3.1 eV and an apparent doping decrease of about four times, as obtained by Capacitance–Voltage measurements, are found. Temperature-dependent luminescence analyses show the quenching of the 3.1 eV band above 200 K, suggesting its donor–acceptor-pair nature. The band onset is interpreted as a result of the Mg dopant instability in the p-type layers, correlated to the device self-heating inducing junction temperature above 300 C. The band is attributed to Mg-related metastable complexes, such as Mg–H₂, acting as shallow acceptors. Due to their unstable nature, the behaviour of the 3.1 eV emission is studied under controlled electron-beam irradiation in the SEM. Its time evolution during 60 min of irradiation reveals an almost complete quenching in the Cathodoluminescence spectra, which is attributed to the dissociation of the Mg–H₂ complexes.