The recombination rate coefficients (RRCs) A, B, and C in MOVPE‐grown single‐quantum‐well light emitting diodes spanning the entire blue‐green spectral range are determined by fitting efficiency curves and differential carrier lifetimes. The results show definite trends for each of the RRCs: A tendentially decreases with increasing wavelength, B definitely decreases, and C remains approximately constant. Therefore, the increase of the droop with increasing wavelength (the green gap problem) is rather due to the decrease of B than an increase of C. The determined values of C are shown to be similar to what has been predicted by others with first‐principles computer simulations accounting for phonon‐assisted Auger recombination. Samples grown on sapphire and silicon substrates are compared and show significant differences only for the RRC A, presumably due to the difference in threading dislocation density.

Internal quantum efficiency (IQE) of a blue highbrightness InGaN/GaN LED was evaluated from the external quantum efficiency measured as a function of current at various temperatures ranged between 13 K and 440 K. Processing the data with a novel evaluation procedure based on the ABC-model, we have determined the temperature dependent IQE of the LED structure and light extraction efficiency of the LED chip. Separate evaluation of these parameters is helpful for further optimization of the heterostructure and chip designs. The data obtained enable making a guess on the temperature dependence of the radiative and Auger recombination coefficients, which may be important for identification of dominant mechanisms responsible for the efficiency droop in III-nitride LEDs. Thermal degradation of the LED performance in terms of the emission efficiency is also considered.

We report the direct observation of hot carriers generated by Auger recombination via photoluminescence spectroscopy on tailored (AlGaIn)N multiple quantum well (QW) structures containing alternating green and ultra-violet (UV) emitting (GaIn)N QWs. Optically pumping solely the green QWs using a blue emitting high power laser diode, carrier densities similar to electrical light-emitting diode (LED) operation were achieved, circumventing possible leakage and injection effects. This way, luminescence from the UV QWs could be observed for excitation where the emission from the green QWs showed significant droop, giving direct evidence for Auger generated hot electrons and holes being injected into the UV QWs. An examination of the quantitative relation between the intensity of the UV luminescence and the amount of charge carriers lost due to drooping of the QWs supports the conclusion that Auger processes contribute significantly to the droop phenomenon in (AlGaIn)N based light-emitting diodes. Due to their high lifetimes and efficiencies along with rapidly declining prices, light-emitting diodes (LEDs) based on (AlGaIn)N multiple quantum well (MQW) structures are on their way to replace incandescent as well as fluorescent lighting. Despite great progress in recent years, resulting in peak power conversion efficiencies of up to 81%, 1 one obstacle still to overcome is the decrease in efficiency towards high operating current densities, a phenomenon commonly known as droop. 2,3 The current dependency of the internal quantum efficiency (IQE) can be modeled in good quantitative agreement with experimental data using an ABC rate equation model [4][5][6]

We obtain temperature-dependent recombination coefficients by measuring the quantum efficiency and differential carrier lifetimes in the state-of-the-art InGaN light-emitting diodes. This allows us to gain insight into the physical processes limiting the quantum efficiency of such devices. In the green spectral range, the efficiency deteriorates, which we assign to a combination of diminishing electronhole wave function overlap and enhanced Auger processes, while a significant reduction in material quality with increased In content can be precluded. Here, we analyze and quantify the entire balance of all loss mechanisms and highlight the particular role of hole localization.