Led Failure Mechanisms And Lifetime

LED Failure Mechanisms and Lifetime

Typically, LEDs do not abruptly croak as most traditional light sources do; instead, their optical skill degrades monotonically over time. In other words, operated at a constant disgust current the amount of light emitted by an LED would simply decrease over time. The rate of adulteration is primarily determined by the drive current and operational temperature of the LED, and the lifetime to a particular amount of degradation give notice be approximated by:
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Where C and n atomic number 18 constants (depending on the selected level of degradation), IF is the drive current, Ea is the thermal activation energy of the LED, k is Boltzmans constant, and Tj is the junction temperature of the LED. The above relationship covers a across-the-board range of degradation mechanisms. The primary degradation mechanisms in LEDs are:

1) Defects in the crystalline structure of the semiconductor material in and near the PN junction called dislocations or dark line deformitys. This defect effectively subjects the quantum efficiency of the LED. GaN-based LEDs are more immune to this effect.
2) admixture diffusion from the electrodes and solder into the semiconductor material.



The effect is that higher drive currents are needed, hence producing higher internal temperatures, both of which reduce lifetime.
3) Reduced performance of phosphors in phosphor-coated LEDs. For example, the Stokes efficiency of the phosphors can be degraded by the absorption of contaminates.
4) insulation of metals in the heat sink bond, often called voiding.
5) moisture absorption into the semiconductor.
6) Electrostatic discharge (ESD) due to poor manipulation and assembly can produce latent defects leading to deepen degradation.
7) Weak or cold wire bonds to the electrodes. These tend to memorialize immediately or within a few hours of operation.If you motivation to get a full essay, order it on our website: Orderessay



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