Optical evidence of an electrothermal degradation of InGaN-based light-emitting diodes during electrical stress

Abstract

The optical properties of blue InGaN-based light-emitting diodes aged at high current levels have been studied by electroluminescence and cathodoluminescence. The onset of a broad optical band peaked at about 3.1 eV in devices aged without a heat sink ~junction temperature higher than 300 °C! has been correlated to an electrothermal threshold effect. The band is attributed to the dissociation of Mg–H complexes inside the p-type layers and to the consequent formation of Mg-related metastable complexes acting as acceptors. Subsequent electron-beam irradiation determines the almost complete quenching of the band

High temperature electro-optical degradation of InGaN/GaN HBLEDs

“…Devices have been stressed at temperatures ranging between 180 and 230°C, with the aim of studying the degradation processes activated at high temperature levels. A number (3)(4)(5)(6)(7)(8) of identical devices were aged at each temperature level, in order to have statistically relevant results. This paper describes the results obtained ageing the samples at 200°C; the devices aged at the other temperature levels showed the same degradation mechanisms, taking place with different kinetics.…”

“…During the last period, many works on LEDs degradation have been published, see for example [1][2][3][4][5][6][7]: in most of the cases, these papers described the behaviour of power LEDs submitted to high current stress. In these cases it is difficult to distinguish whether detected degradation effects are ascribable to carrier flow or to high temperatures reached by the junction during stress, and a model for thermal degradation of the devices cannot be efficiently derived.…”

Effect of long-term aging on series resistance and junction conductivity of high-power InGaN light-emitting diodes

“…The decrease in series resistance could be attributed to continuous annealing of the p cladding layer in the light-emitting structure. Such a post-fabrication self-annealing can result in a higher density of holes due to the instability of residual Mg-H complexes [21][22][23] and might be more pronounced in high-power LEDs operating at increased junction temperatures. However, the junction temperature of 350 K is too low to invoke conventional breakdown of the Mg-H complexes, which are known to dissociate at about 1000 K [24].…”

Remote temperature mapping of high-power InGaN/GaN MQW flip-chip design LEDs

“…Firstly, the giant temperature gradient inside a multiple layer structure with different expansion coefficients could cause local irreversible mechanical stress of the p-n junction and provoke a catastrophic device failure 10 . Secondly, electrical and thermal effects combined could result in an activation of non-radiative recombination process through generation of active acceptors in p-GaN layer 11 .…”