Degradation mechanism of light-emitting diodes on patterned sapphire substrate

We have investigated possible degradation mechanism for patterned sapphire substrate (PSS)-based blue light-emitting diodes (LEDs) using an acceleration burn-in test under high current stress. Normal LEDs without a PSS had also been compared. Measurements showed that the PSS-LED has lower series resistance and higher output power compare to those of the normal LED. The acceleration test (@ 490 mA/cm(2)) results showed that the normal LED suffers from current crowding irrespective of acceleration time while the PSS LED endures up to 100 s. In addition, the estimated lifetime of the PSS-LED is 1.6 times as high as that of the normal LED at high electrical stress of 490 A/cm(2), indicating that the PSS-LED shows excellent reliability characteristics. Based on electrical/optical measurement results, acceleration test data, and Auger depth profile results, possible degradation mechanism of the PSS-LED will be discussed in terms of junction temperature (originating from Joule heating), carrier crowding, and p-contact failure. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim