In recent years, point defects (PDs) have been unveiled as critical nonradiative recombination centres in InGaN/GaN quantum wells (QWs). When left unchecked, these nonradiative PDs can lead to at least an order-of-magnitude reduction in the internal quantum efficiency of blue light-emitting diodes. While macroscale studies have provided some information on such critical PDs, much deeper insight could be obtained by directly accessing the nanoscale impact of PDs on QW optical properties.
Here, we present a detailed investigation of nonradiative PDs in a series of single InGaN/GaN QWs. Applying time-resolved cathodoluminescence (TRCL), we map the evolution of QW CL intensity spatially and temporally with nanometre and sub-nanosecond resolution, pinpointing individual PD locations. We fit the CL decays around single PDs with a carrier diffusion-recombination model to fully quantify their intrinsic properties, including novel phonon-limited relaxation times.
We study the impact of non-radiative defects on Auger recombination in c-plane InGaN/GaN single quantum wells (SQWs) in the efficiency droop regime using high injection time-resolved photoluminescence. The defect density in the active layer is tuned by varying the thickness of an InAlN underlayer. When the defect density is increased, apart from Shockley–Read–Hall (SRH) and standard Auger recombination, introducing an extra defect-assisted Auger process is required to reconcile the discrepancy observed between the usual ABC model and experimental data. We derive a linear dependence between the SRH coefficient and the bimolecular defect-assisted Auger coefficient, which suggests that the generated defects can act as scattering centers responsible for indirect Auger processes. Our results further suggest that the defect-assisted Auger recombination is expected to be all the more critical in green to red III-nitride light-emitting diodes due to their reduced radiative rate.
The success story of blue light-emitting diodes over the past decade is underpinned by the high internal quantum efficiency (IQE) of the InGaN/GaN quantum wells (QWs) within the active region. Yet this extraordinary IQE can only be achieved by adding an indium-containing layer before the QWs—the “underlayer” (UL). In this work, we evidence that any indium-containing III-nitride layer acts to incorporate surface defects; the UL hence acts as a getter for surface defects to avoid their incorporation into the QWs as IQE-reducing point defects (PDs). We directly observe the reduction in PD-density caused by increasing the UL thickness.
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