Temperature and injection current dependence of electroluminescence intensity in green and blue InGaN single-quantum-well light-emitting diodes

Abstract

Temperature and injection current dependence of electroluminescence (EL) spectral intensity of the superbright green and blue InGaN single-quantum-well (SQW) light-emitting diodes has been studied over a wide temperature range (T=15−300 K) and as a function of injection current level (0.1–10 mA). It is found that, when temperature is slightly decreased to 140 K, the EL intensity efficiently increases in both cases, as usually seen due to the improved quantum efficiency. However, with further decrease of temperature down to 15 K, unusual reduction of the EL intensity is commonly observed for both of the two diodes. At low temperatures the integrated EL intensity shows a clear trend of saturation with current, accompanying decreases of the EL differential quantum efficiency. We attribute the EL reduction due to trapping of injected carriers by nonradiative recombination centers. Its dependence on temperature and current shows a striking difference between the green and blue SQW diodes. That is, we find that the blue InGaN SQW diode with a smaller In concentration shows more drastic reduction of the EL intensity at lower temperatures and at higher currents than the green one. This unusual evolution of the EL intensity with temperature and current is due to less efficient carrier capturing by SQW. The carrier capture in the green and blue diodes also shows a keen difference owing to the different In content in the InGaN well. These results are analyzed within a context of rate equation model, assuming a finite number of radiative recombination centers. Importance of the efficient carrier capture processes by localized tail states within SQW at 180–300 K is thus pointed out for explaining the observed enhancement of radiative recombination of injected carriers in the presence of high-density misfit dislocations.