Radiative recombination mechanisms in polar and non-polar InGaN/GaN quantum well LED structures

Abstract

We study the photoluminescence internal quantum efficiency (IQE) and recombination dynamics in a pair of polar and nonpolar InGaN/GaN quantum well (QW) light-emitting diode (LED) structures as a function of excess carrier density and temperature. In the polar LED at 293K, the variation of radiative and non-radiative lifetimes is well described by a modified ABC type model which accounts for the background carrier concentration in the QWs due to unintentional doping. As the temperature is reduced, the sensitivity of the radiative lifetime to excess carrier density becomes progressively weaker. We attribute this behaviour to the reduced mobility of the localised electrons and holes at low temperatures, resulting in a more monomolecular like radiative process. Thus we propose that in polar QWs, the degree of carrier localisation determines the sensitivity of the radiative lifetime to the excess carrier density. In the non-polar LED, the radiative lifetime is independent of excitation density at room temperature, consistent with a wholly excitonic recombination mechanism. These findings have significance for the interpretation of LED efficiency data within the context of the ABC recombination model. *

Impact of superlinear defect-related recombination on LED performance at low injection

“…It has been shown that radiative recombination in polar InGaN/ GaN QWs grown on c-plane sapphire substrates is bimolecular, meaning that excitonic effects can be neglected. 23 Since our LEDs are grown this way, we assume that the radiative recombination rate in the active QWs is equal to Bn 2 , where B 300 = 1 × 10 −10 cm 3 s −1 is the radiative recombination coefficient at room temperature (300 K) and n is the photoexcited carrier density. 5,6,12 We note that this estimate for B includes corrections that are required to accommodate photon recycling, 24 which will vary with device structure and optical design.…”

Effects of Wavelength and Defect Density on the Efficiency of (In,Ga)N-Based Light-Emitting Diodes

“…A fundamental assumption of the ABC model is, that the three coefficients A, B, and C are constant. However, there are recent indications that this is not necessarily the case, for instance the non-radiative lifetime (inverse of A) increases with increasing carrier density [24][25][26]. Also the radiative recombination is expected to increase at high current densities, when screening of the internal fields in the QW increases the wave function overlap (and thus B).…”

InGaN/GaN Structures: Effect of the Quantum Well Number on the Cathodoluminescent Properties

“…We have identified two bands in PL spectra of our structures, the faster blue and a slower defect bands, which differ by most properties, such as by their spectral position and width, lifetime, and sensitivity to diverse type of excitation. The fast blue QW band has luminescence time in the order of nanoseconds and has probably still excitonic nature, as our QWs are designed to be shallow and thin . The slower defect band has luminescence response in the microsecond time scale which is not desired in fast scintillator applications.…”

“…The fast blue QW band has luminescence time in the order of nanoseconds and has probably still excitonic nature, as our QWs are designed to be shallow and thin. [6] The slower defect band has luminescence response in the microsecond time scale which is not desired in fast scintillator applications. Although luminescent nitride structures have been widely used for a long time, the luminescent properties of the defect bands in bulk GaN and InGaN/GaN QW structures are not well understood, because this defect band can be observed only for very low excitation densities which are not subject of interest for LED focused research.…”

“…10 18 to 10 22 cm À3 s À1 , which are several order of magnitude lower than in the case of typical LED excitation (10 24 -10 28 cm À3 s À1 ). [6] Many works have focused on the defects in GaN responsible for the slow "yellow band." [7,8] To the best of our knowledge, the origin of the blue or green defect bands from InGaN QWs has not been explained so far.…”