Gradual Degradation of InGaAs LEDs: Impact on Non-Radiative Lifetime and Extraction of Defect Characteristics

Abstract

We present a detailed analysis of the gradual degradation mechanisms of InGaAs Light-Emitting Diodes (LEDs) tuned for optical emission in the 1.45–1.65 μm range. Specifically, we propose a simple and effective methodology for estimating the relative changes in non-radiative lifetime, and a procedure for extracting the properties of defects responsible for Shockley-Read-Hall recombination. By means of a series of accelerated aging experiments, during which we evaluated the variations of the optical and electrical characteristics of three different families of LEDs, we were able to identify the root causes of device degradation. Specifically, the experimental results show that, both for longer stress time at moderate currents or for short-term stress under high injection levels, all the devices are affected: (i) by a partial recovery of the optical emission at the nominal bias current; and (ii) by a decrease in the emission in low-bias regime. This second process was deeply investigated, and was found to be related to the decrease in the non-radiative Shockley-Read-Hall (SRH) lifetime due to the generation/propagation of defects within the active region of the LEDs. Devices tuned for longer-wavelength emission exhibited a second degradation process, which was found to modify the carrier injection dynamics and further speed-up optical degradation in the low bias regime. These processes were ascribed to the effects of a second non-radiative recombination center, whose formation within the active region of the device was induced by the aging procedure. Through mathematical analysis of the degradation data, we could quantify the percentage variation in SRH lifetime, and identify the activation energy of the related defects.

Degradation- and Thermal-Related Changes in Selected Electro-Optical Parameters of High-Power 270–280 nm LEDs

“…Our research results indicate that a lower ∆P n.∆I of UVC LEDs occurred when LEDs were supplied with higher current (Figure 5), which means an increase in the junction temperature [20,51]. The observed rapid drop in the ∆OP n.∆I coefficient for low currents after degradation may be caused by the increase in nonradiative recombination.…”

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“…At low current levels, LED B had a slope of about 2, indicating a regime where non-radiative recombination prevails [27,28]. LED D showed a lower slope but it presented the highest increase, which could be ascribed to a stronger generation of non-radiative centers in the device [28]. The same behavior could be found in the other two LEDs, indicating that optical degradation may be partially correlated to a defect generation.…”

“…For LED B and D, the slopes increased with stress time, indicating a stronger contribution of non-radiative recombination processes also in high carrier injection conditions. At low current levels, LED B had a slope of about 2, indicating a regime where non-radiative recombination prevails [27,28]. LED D showed a lower slope but it presented the highest increase, which could be ascribed to a stronger generation of non-radiative centers in the device [28].…”

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“…When measured at high current, all devices presented a slope of about 1 before the stress, which can be associated with the regime where the radiative recombination prevails; as the stress time proceeds the slope tends to increase, and at higher stress currents the increase is steeper, suggesting a correlation with the growth of Shockley-Read-Hall (SRH) recombination rate. [15] The slopes measured at low current levels have an initial slope of 2 or higher, which indicates that the devices are operating in the regime where prevails nonradiative recombination processes [16,17] and possibly asymmetrical injection. [18] The low current L-I slopes presented an increasing trend during the aging similar to the high current ones.…”