InGaN-based optoelectronic devices: Loss mechanisms and degradation processes

This paper reviews the physical mechanisms that limit the performance and the reliability of visible InGaN-based LEDs and laser diodes. The results of an extensive experimental activity demonstrate that: (i) point defects may significantly affect the optical efficiency of GaN-based LEDs and lasers, by favoring the Shockley-Read-Hall recombination in the active region of the samples; hypothesis on the physical nature of the defects were formulated based on deep-level transient spectroscopy measurements. (ii) extended defects (such as threading dislocations) represent preferential paths for leakage current conduction, and may severely limit the reliability of LEDs submitted to reverse-bias ESD tests; (iii) when submitted to constant current stress, InGaN-based LEDs and laser diodes may show a measurable degradation, consisting in a decrease in optical power (or increase in the threshold current of laser diodes) and in changes in the electrical characteristics. The degradation kinetics are significantly accelerated by current density and temperature, indicating that - in several cases - the degradation processes are electro-thermally activated.