Blue LEDs – way to overcome efficiency droop



In this paper we report on fabrication of high power InGaN based blue light emitting diodes (LEDs) with substantially suppressed efficiency droop. The key feature of proposed device is the utilization of short-period superlattice in the active region of LED heterostructure. In this superlattice the GaN barriers between quantum wells (QWs) are transparent for tunnelling, thus enabling carrier delocalization in growth direction. This, in turn, leads to the reduction of carrier concentration at given pumping comparing to the standard LED heterostructure, where, usually, only one QW contributes to light emission. The reduction of carrier concentration results in substantial suppression of third order non-radiative processes, such as Auger recombination, responsible for the efficiency droop at high pumping. As a result, the LED external efficiency at operating current 350 mA differs from its maximum value only by 7%. Also, fabricated LEDs demonstrate very good stability of spectral position of the emission line, the observed blue shift of electroluminescence being less than 1 nm at pumping up to 1000 mA. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)