Abstract
AbstractThis paper analyzes the effects of ageing on 1 W 420 nm GaN LEDs. Devices have been subjected to 350 mA dc stress at fixed case temperatures (60‐100 °C). Results indicate that two different ageing mechanisms take place during ageing: (i) a fast decrease in capacitance well correlated with the increase in series resistance of the device; this effect is probably related with a rapid p‐type doping decrease caused by the flow of carrier through the Mg doped region, and (ii) a gradual but substantial increase of the low current optical output during the ageing; only slight decrease is instead detected in the high current region. A possible explanation could be the increase of injected current efficiency related to a decrease of low forward bias diagonal tunnelling (DT) during ageing. This hypothesis is supported by a variation of the charge distribution in the quantum well region during ageing. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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