Low-frequency noise in as-fabricated and degraded blue InGaAs/GaN LEDs

Abstract

Study of the spectral noise density and its dependence on current density in as fabricated and degraded blue light emitting diodes (LEDs) based on InGaN/GaN quantum well structures are reported. It is shown that defects are generated nonuniformly in the course of degradation, being concentrated along extended defects penetrating into the active region of LEDs. It is demonstrated that the decrease in the exter nal quantum efficiency in the course of aging is due to the enhancement of charge transport uniformity, which leads to the formation of shunts and local overheating regions. Typically, in blue LEDs, these effects are responsible for the ambiguous development of the degradation process, which hinders prognostication of LED service life. The effect of noise suppression is observed in a narrow current density range (10 -2 to 10 -1 A cm -2 ) corresponding to the onset of radiative recombination.

Failure mechanisms in blue InGaN/GaN LEDs for high power operation

“…The gradual non-uniform accumulation of defects results in formation of current leakage paths and local hot spots which had been observed in many studies [1,3,11].…”

“…It should be noted that, for further LED degradation, local overheating regions (channels) that appear in the diodes were observed by IR imaging microscopy [11]. Increasing non-uniform current distribution causing local overheating enables the migration of gallium and indium metal impurity ions along the system of extended defects penetrating through the LED active region.…”

Review of Low-Frequency Noise Properties of High-Power White LEDs during Long-Term Aging

“…Materials 2021, 14, x FOR PEER REVIEW 12 of 20 due to migration of defects at high aging current and related to increase of the sample temperature due to Joule heating. Apparent defect migration and penetration into the LED active area due to local overheating and non-uniform charge carrier transport has been observed in blue InGaN LEDs during accelerated aging in a much shorter time interval of the experiment from 280 h to 1000 h [33]. The emitted light spectra after 8000 h of aging are presented in Figure 12.…”

“…During aging in the time interval from 4000 h to 8000 h, the noise intensity demonstrates unstable behavior caused by formation of localized states of defects in the barrier layers of the QWs due to migration of defects at high aging current and related to increase of the sample temperature due to Joule heating. Apparent defect migration and penetration into the LED active area due to local overheating and non-uniform charge carrier transport has been observed in blue InGaN LEDs during accelerated aging in a much shorter time interval of the experiment from 280 h to 1000 h [ 33 ].…”

“…The low-frequency electrical and optical noise characteristics of white nitride-based LEDs, their quality, and their reliability during long-term aging at normal operation condition at room temperature (RT) were extensively investigated in [ 18 , 26 , 27 , 28 , 29 , 30 ]. There are studies of other research groups where low-frequency noise and degradation mechanisms of nitride-based LEDs during aging have been analyzed [ 15 , 17 , 31 , 32 , 33 , 34 ]. The conditions and types of different aging experiments performed together with the low-frequency noise investigation are presented in Table 1 .…”