"Electrical Properties, Reliability Issues, and ESD Robustness of InGaN-Based LEDs" in III-Nitride Based Light Emitting Diodes and Applications

This chapter describes the physical mechanisms that may induce the degradation of InGaN-based LEDs. Before going into a detailed description of the main degradation processes, we will give a brief overview on the electrical (current-voltage) characteristics of LEDs, to provide the basic information which is useful to understand the electrical characterization data reported in the subsequent part of the chapter. On the basis of literature data, we will analyze the main mechanisms responsible for current conduction, with focus on tunneling mechanisms, reverse-current conduction, and on the origin of the high ideality factors, always present in InGaN LEDs. After this introductory section, we will discuss the main physical mechanisms that may limit the lifetime of GaN-based LEDs submitted to short and long-term operation. More specifically, we will focus on the following mechanisms: (i) the degradation of the blue semiconductor chip, due to the generation of non-radiative recombination centers, and to the degradation of the p-type semiconductor and contacts; (ii) the degradation mechanisms that affect the performance of the package and phosphors, which are typically activated at high temperature levels; and (iii) the failure of LEDs submitted to ElectroStatic Discharges (ESD)