Cathodoluminescence in the scanning transmission electron microscope

Cathodoluminescence technique combined with transmission electron microscopy (TEM-CL) has been used to characterize optical properties of dislocations in GaN epilayers. The dislocations act as nonradiative centers with different recombination rates. TEM-CL observation showed that even for the same Burgers vector of a, the dislocations show different electrical activity depending on the direction of dislocation line, i.e., the edge-type dislocation parallel to the c plane is very active, while the screw-type one is less active. The simulation of the CL images gives us the information of parameters such as carrier lifetime and diffusion length. (C) 2003 American Institute of Physics.

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Cathodoluminescence characterization of dislocations in gallium nitride using a transmission electron microscope - eScholarship

Monolayer two-dimensional transitional metal dichalcogenides, such as MoS2, WS2, and WSe2, are direct band gap semiconductors with large exciton binding energy. They attract growing attentions for optoelectronic applications including solar cells, photodetectors, light-emitting diodes and phototransistors, capacitive energy storage, photodynamic cancer therapy, and sensing on flexible platforms. While light-induced luminescence has been widely studied, luminescence induced by injection of free electrons could promise another important applications of these new materials. However, cathodoluminescence is inefficient due to the low cross-section of the electron–hole creating process in the monolayers. Here for the first time we show that cathodoluminescence of monolayer chalcogenide semiconductors can be evidently observed in a van der Waals heterostructure when the monolayer semiconductor is sandwiched between layers of hexagonal boron nitride (hBN) with higher energy gap. The emission intensity shows a str...

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Giant enhancement of cathodoluminescence of monolayer transitional metal dichalcogenides semiconductors

Nitride-based three-dimensional core–shell nanorods (NRs) are promising candidates for the achievement of highly efficient optoelectronic devices. For a detailed understanding of the complex core–shell layer structure of InGaN/GaN NRs, a systematic determination and correlation of the structural, compositional, and optical properties on a nanometer-scale is essential. In particular, the combination of low-temperature cathodoluminescence (CL) spectroscopy directly performed in a scanning transmission electron microscope (STEM), and quantitative high-angle annular dark field imaging enables a comprehensive study of the nanoscopic attributes of the individual shell layers. The investigated InGaN/GaN core–shell NRs, which were grown by metal–organic vapor-phase epitaxy using selective-area growth exhibit an exceptionally low density of extended defects. Using highly spatially resolved CL mapping of single NRs performed in cross-section, we give a direct insight into the optical properties of the individual co...

Nanoscopic Insights into InGaN/GaN Core–Shell Nanorods: Structure, Composition, and Luminescence

The dependence of excited electron–hole state properties on the size of their host semiconducting nanostructures is the seed for a plethora of applications such as light-emitting diodes (LEDs) and photovoltaic cells. However, the inability of state-of-the art, diffraction-limited optical techniques to probe lifetime variations at the scale of individual quantum emitters precludes the full understanding of the nanostructures’ optical properties. Here, we demonstrate the measurement of the individual lifetimes of quantum emitters a few angstroms thick separated by only a few nanometers, lifting the ambiguities usually faced by diffraction-limited techniques. This relies on the ability to monitor with subnanometer precision a fast electron beam that triggers extremely localized cathodoluminescence signals further analyzed through intensity interferometry (spatially resolved time-correlated cathodoluminescence, SRTC-CL). We demonstrate SRTC-CL to be a true nanometer counterpart of time-resolved photoluminesce...

Lifetime Measurements Well below the Optical Diffraction Limit

Nanocathodoluminescence reveals the spectral properties of individual InGaN quantum wells in high efficiency light emitting diodes. We observe a variation in the emission wavelength of each quantum well, in correlation with the Si dopant concentration in the quantum barriers. This is reproduced by band profile simulations, which reveal the reduction of the Stark shift in the quantum wells by Si doping. We demonstrate nanocathodoluminescence is a powerful technique to optimize doping in optoelectronic devices.

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Nanocathodoluminescence Reveals Mitigation of the Stark Shift in InGaN Quantum Wells by Si Doping.

This work was carried out with the support of the United
Kingdom Engineering and Physical Sciences Research Council
under Grant Nos EP/NO17927/1 and EP/J003603/1 R Oliver
acknowledges funding from the European Research Council
under the European Community’s Seventh Framework
Programme (FP7/2007-2013) ERC grant agreement number
279361 (MACONS) and the from the Royal Academy of
Engineers/Leverhulme Trust senior research fellowship This
research is conducted in part using the research computing
facilities offered by Information Technology Services at the
University of Hong Kong

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David Stowe

Papers

Nanocathodoluminescence Reveals Mitigation of the Stark Shift in InGaN Quantum Wells by Si Doping.

Nano-cathodoluminescence reveals the effect of electron damage on the optical properties of nitride optoelectronics and the damage threshold