Reliability of Ultraviolet Light Emitting Diodes
This chapter presents an extensive review of the literature on the degradation processes of GaN based UV A, UV B, and UV C LEDs. For the state of the art devices, the main open issue is the increase in Shockley Read Hall non radiative recombination inside the quantum well, originating from local generation of defects or from diffusion processes of dopant atoms or foreign impurities. Temperature acts as a significant acceleration factor, especially in lower wavelength devices, affected by a higher turn on voltage. Changes in the chemical structure of the package and of the encapsulant, induced by the high energy of the photons, may lead to a lower reflectivity and transmittance, thus limiting the overall reliability of the devices.