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.
The diffraction based scanning electron microscopy (SEM) technique of electron channeling contrast imaging (ECCI) provides rapid and non-destructive information on defects on length scales from tens of nanometres to tens of micrometres. ECCI may be complemented by electron backscatter diffraction (EBSD) and hyperspectral cathodoluminescence imaging (CL). EBSD provides orientation, phase, polarity and strain information, whilst CL reveals the influence of phase, composition, strain and defects on luminescence. I will discuss our recent investigations of phase, composition and polarity, the type, density and distribution of defects and the distribution of strain in a range of nitride semiconductor structures.
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