Injection-limited efficiency of InGaN LEDs and impact on electro-optical performance and ageing: a case study

This paper investigates the factors that influence the efficiency and reliability of InGaN based visible light emitting diodes with non-optimized carrier injection. The devices under test are LEDs with a single quantum well with a nominal emission wavelength of 495 nm at I = 100 mA. We stressed the devices with a constant current density of J = 80 A/cm2, at room temperature, for 25000 minutes. We monitored the optical performance of the devices before and during stress. From the preliminary characterization we observed an increment in the optical power followed by a blue shift as a function of current. Simulation results highlight an asymmetric carrier injection, in particular a lack of electrons in the low bias regime. The low injection efficiency is also confirmed by temperature-dependent measurements, where we observed an increment in the OP with increasing temperature. During an ageing experiment, we observed an increment in OP for high injection level, accompanied with a blue shift in the peak emission wavelength. This result suggests an improvement in the injection efficiency and or a better carrier confinement. In this regard, we performed photoluminescence measurements during stress, which confirm the hypothesis of a better carrier confinement. In particular, PL signal show an increasing trend during the ageing process, which can be ascribed to the generation of negatively charged defects in the quantum barrier, with consequent impact on carrier confinement.