Efficiency Drop in GreenInGaN/GaNLight Emitting Diodes: The Role of Random Alloy Fluctuations (original) (raw)
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Simulation of random alloy effects in InGaN/GaN LEDs
2013 13th International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD), 2013
We present atomistic simulations of InGaN quantum disk and quantum well structures considering randomly distributed In atoms. It is shown that the random alloy fluctuations lead to an intrinsic broadening of the optical emission lines with an asymmetric tail towards long wavelengths. The amount of broadening is found to be dependent on In content.
Journal of Applied Physics, 2014
In this paper, we describe the influence of the intrinsic indium fluctuation in the InGaN quantum wells on the carrier transport, efficiency droop, and emission spectrum in GaN-based light emitting diodes (LEDs). Both real and randomly generated indium fluctuations were used in 3D simulations and compared to quantum wells with a uniform indium distribution. We found that without further hypothesis the simulations of electrical and optical properties in LEDs such as carrier transport, radiative and Auger recombination, and efficiency droop are greatly improved by considering natural nanoscale indium fluctuations. V
2014
Electroluminescence (EL) characterization of InGaN/GaN light-emitting diodes (LEDs), coupled with numerical device models of different sophistication, is routinely adopted not only to establish correlations between device efficiency and structural features, but also to make inferences about the loss mechanisms responsible for LED efficiency droop at high driving currents. The limits of this investigative approach are discussed here in a case study based on a comprehensive set of currentand temperature-dependent EL data from blue LEDs with low and high densities of threading dislocations (TDs). First, the effects limiting the applicability of simpler (closed-form and/or one-dimensional) classes of models are addressed, like lateral current crowding, vertical carrier distribution nonuniformity, and interband transition broadening. Then, the major sources of uncertainty affecting state-ofthe-art numerical device simulation are reviewed and discussed, including (i) the approximations in the transport description through the multi-quantum-well active region, (ii) the alternative valence band parametrizations proposed to calculate the spontaneous emission rate, (iii) the difficulties in defining the Auger coefficients due to inadequacies in the microscopic quantum well description and the possible presence of extra, non-Auger high-current-density recombination mechanisms and/or Auger-induced leakage. In the case of the present LED structures, the application of three-dimensional numerical-simulation-based analysis to the EL data leads to an explanation of efficiency droop in terms of TD-related and Auger-like nonradiative losses, with a C coefficient in the 10 −30 cm 6 /s range at room temperature, close to the larger theoretical calculations reported so far. However, a study of the combined effects of structural and model uncertainties suggests that the C values thus determined could be overestimated by about an order of magnitude. This preliminary attempt at uncertainty quantification confirms, beyond the present case, the need for an improved description of carrier transport and microscopic radiative and nonradiative recombination mechanisms in device-level LED
Local indium segregation and band structure in high efficiencygreen light emitting InGaN/GaN diodes
Solid State Communications - SOLID STATE COMMUN, 2004
GaN/InGaN light emitting diodes (LEDs) are commercialized for lighting applications because of the cost efficient way that they produce light of high brightness. Nevertheless, there is significant room for improving their external emission efficiency from typical values below 10 percent to more than 50 percent, which are obtainable by use of other materials systems that, however, do not cover the visible spectrum. In particular, green-light emitting diodes fall short in this respect, which is troublesome since the human eye is most sensitive in this spectral range. In this letter advanced electron microscopy is used to characterize indium segregation in InGaN quantum wells of high-brightness, green LEDs (with external quantum efficiency as high as 15 percent at 75 A/cm2). Our investigations reveal the presence of 1-3 nm wide indium rich clusters in these devices with indium concentrations as large as 0.30-0.40 that narrow the band gap locally to energies as small as 2.65 eV.
Two channels of non-radiative recombination in InGaN/GaN LEDs
Physica B: Condensed Matter, 2009
The results of low-frequency noise study in blue InGaN/GaN light emitting diodes (LEDs) allow to suppose that there are two non-radiative recombination channels in InGaN/GaN LEDs: one of them is related to the extended defect system piercing the LED active region and other is related with the presence of point defects. The generation of new defects under current density more than 10 A/cm 2 was found. This process is reversible up to operation current density of about 200 A/cm 2 .
Recombination Pathways in Green InGaN/GaN Multiple Quantum Wells
Nanoscale research letters, 2017
This paper reports the transient photoluminescence (PL) properties of an InGaN/GaN multiple quantum well (MQW) light-emitting diode (LED) with green emission. Recombination of localized excitons was proved to be the main microscopic mechanism of green emission in the sample. The PL dynamics were ascribed to two pathways of the exciton recombination, corresponding to the fast decay and the slow decay, respectively. The origins of slow decay and fast decay were assigned to local compositional fluctuations of indium and thickness variations of InGaN layers, respectively. Furthermore, the contributions of two decay pathways to the green PL were found to vary at different emission photon energy. The fraction of fast decay pathway decreased with decreasing photon energy. The slow radiative PL from deep localized exciton recombination suffered less suppression from non-radiative delocalization process, for the higher requested activation energy. All these results supported a clear microsco...
2006
High efficient green light emitting diodes (LED) on the basis of GaN/InGaN exhibit indium-rich nanoclusters inside the quantum wells (QW) due to InN-GaN phase decomposition. By direct measurements of the variations in the electronic structure, we show for the first time a correlation between indium-rich nanoclusters and local energy band gap minima. Our investigations reveal the presence of 1-3 nm wide indium rich clusters in these devices with indium concentrations x as large as xw0.30-0.40 that narrow the band gap locally to energies as small as 2.65 eV. These clusters are able to act as local traps for migrating photon-emitting carriers and seem to boost the overall device performance. q
Internal quantum efficiency and tunable colour temperature in monolithic white InGaN/GaN LED
Gallium Nitride Materials and Devices IX, 2014
Internal Quantum Efficiency (IQE) of two-colour monolithic white light emitting diode (LED) was measured by temperature dependant electro-luminescence (TDEL) and analysed with modified rate equation based on ABC model. External, internal and injection efficiencies of blue and green quantum wells were analysed separately. Monolithic white LED contained one green InGaN QW and two blue QWs being separated by GaN barrier. This paper reports also the tunable behaviour of correlated colour temperature (CCT) in pulsed operation mode and effect of self-heating on device performance.