A novel hybrid inorganic/organic semiconductor nanostructure has been developed, leading to very efficient nonradiative resonant-energy-transfer (RET) between blue emitting InGaN/GaN multiple quantum wells (MQWs) and a yellow light emitting polymer. The utilization of InGaN/GaN nanorod arrays allows for both higher optical performance of InGaN blue emission and a minimized separation between the InGaN/GaN MQWs and the emitting polymer as a color conversion medium. A significant reduction in decay lifetime of the excitons in the InGaN/GaN MQWs of the hybrid structure has been observed as a result of the nonradiative RET from the nitride emitter to the yellow polymer. A detailed calculation has demonstrated that the efficiency of the nonradiative RET is as high as 73%. The hybrid structure exhibits an extremely fast nonradiative RET with a rate of 0.76 ns(-1), approximately three times higher than the InGaN/GaN MQW nonradiative decay rate of 0.26 ns(-1). It means that the RET dominates the nonradiative processes in the nitride quantum well structure, which can further enhance the overall device performance.

Excitonic recombination dynamics has been investigated on a series of InxGa1−xN/GaN (0.10 ≤ x ≤ 0.30) nanorod (NR) structures with a diameter of ∼220 nm by time-revolved photoluminescence (PL). The NR structures are fabricated by means of a post-growth etching technique. Compared with their corresponding as-grown samples, the time-integrated PL intensities of the NR samples show a remarkable enhancement with a factor of up to 52 at room temperature. The ratios of the radiative to non-radiative recombination lifetime of the NR structures are much less sensitive to temperature than those of their corresponding as-grown samples. This becomes more prominent with increasing indium composition. A distinct delay in transition temperature, where the dominating emission mechanism changes from radiative to non-radiative recombination, has been observed on the NR structures. The great enhancement in optical properties is attributed to both strain relaxation and extra in-plane excitonic confinement due to the nanostructures.

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Cross-sectional sizes and emission wavelengths of regularly patterned GaN and core-shell InGaN/GaN quantum-well nanorod arrays Discrimination of local radiative and nonradiative recombination processes in an InGaN/GaN single-quantum-well structure by a time-resolved multimode scanning near-field optical microscopy

The scanning electron microscopy techniques of electron backscatter diffraction (EBSD), electron channelling contrast imaging (ECCI) and cathodoluminescence (CL) hyperspectral imaging provide complementary information on the structural and luminescence properties of materials rapidly and non-destructively, with a spatial resolution of tens of nanometres. EBSD provides crystal orientation, crystal phase and strain analysis, whilst ECCI is used to determine the planar distribution of extended defects over a large area of a given sample. CL reveals the influence of crystal structure, composition and strain on intrinsic luminescence and/or reveals defect-related luminescence. Dark features are also observed in CL images where carrier recombination at defects is non-radiative. The combination of these techniques is a powerful approach to clarifying the role of crystallography and extended defects on a material’s light emission properties. Here we describe the EBSD, ECCI and CL techniques and illustrate their use for investigating the structural and light emitting properties of UV-emitting nitride semiconductor structures. We discuss our investigations of the type, density and distribution of defects in GaN, AlN and AlGaN thin films and also discuss the determination of the polarity of GaN nanowires.