Cathodoluminescence system offers quantitative and reliable data for optoelectronics devices
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Cathodoluminescence system offers quantitative and reliable data for optoelectronics devices The pitch The increasing demand for new optoelectronics devices such as solar cells, laser diodes (LD), and high-brightness light-emitting diodes (HBLED) combined with the economic necessity to achieve lower consumption levels and higher yields are motivating researchers to develop new materials. Specifically many studies are being initiated to improve the understanding of the fundamental physical properties and behavior of compound semiconductor materials including quantum wells, quantum dots, and nanowire-like structures. An innovative method of cathodoluminescence (CL) is required to generate reliable, quantitative, and stable data as well as to prepare the basis for quality control during production. Conventionally, CL is a challenging technique generally carried out using unwieldy laboratory-assembled devices. A
scanning electron microscope (SEM) is required along with a CL add-on device consisting of a light-collection mirror and a detection system. Both of these must be assembled together, which can result in cumbersome and unstable alignment plus interfacing difficulties. This is particularly the case with cryogenic positioning stages. The collection mirror (parabolic or elliptic) has a very limited field of view (several micrometers), thus when the sample is moved slightly, most of the signal is lost and realignment is required. In addition, the light collection efficiency is very low because the photons collected are dispersed when they are not exactly collected at the focal point of the mirror, which results in limited sensitivity. The company Attolight makes CL available in a simplified system that integrates CL with both light and electron microscopy. It features a hyperspectral imaging mode that reveals ultra-trace impurities and crystallographic defects not visible using other imaging modalities. At production sites, it is expected to become a major tool for detecting defective materials at an early stage of the manufacturing process thereby generating significant savings.
The technology Cathodoluminescence characterization of a GaAs pyramid sample. The spectrum shows five main peaks corresponding to the five main structures in the pyramid. These are, from low to high energy: the quantum dot at the tip of the pyramid (QD), the vertical quantum wire (VQWR), the lateral quantum wires (QWR), the vertical quantum wells (VQW), and the quantum well along the sides of the pyramid (QW). SE is secondary electrons.
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MRS BULLETIN
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VOLUME 36 • DECEMBER 2011
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www.mrs.org/bulletin
The Attolight system is an independent spectroscopy system in which a light microscope is embedded within the electron objective lens of an SEM; both fields
of vision match each other. The light microscope visually positions the system so no optical alignment is required. This innovative design is optimized to achieve superior CL performance without compromising SEM performance. For example, secondary electrons are not obstructed b
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