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III-Nitride Materials and Characterization
Published in Wengang (Wayne) Bi, Hao-chung (Henry) Kuo, Pei-Cheng Ku, Bo Shen, Handbook of GaN Semiconductor Materials and Devices, 2017
Bo Shen, Ning Tang, XinQiang Wang, ZhiZhong Chen, FuJun Xu, XueLin Yang, TongJun Yu, JieJun Wu, ZhiXin Qin, WeiYing Wang, YuXia Feng, WeiKun Ge
Cathodoluminescence (CL) is a phenomenon of photon emission when electrons are impacting on a luminescent material. Similar to PL, CL is a spontaneous light emission from radiative recombination of nonequilibrium carriers and usually used to study the emission mechanisms and characterize the properties of materials with impingement of a high energy electron beam. CL measurements are performed in an electron microscope equipped with a CL detector. As sketched in Figure 1.39, a sample is impinged by a focused electron beam and the emitted light is collected by an optical system, such as a parabolic mirror. Through the detection of monochromatic light passing through a spectrometer by PMT or CCD, the CL spectrum can be obtained. By moving the electron beam on the surface of a sample and measuring the light emitted at each point, the optical activity of the specimen can be mapped.
x Te 1by measurement of the [111] zone axis critical voltage
Published in A G Cullis, P D Augustus, Microscopy of Semiconducting Materials, 1987, 2021
A critical voltage occurs when two branches of the high energy electron dispersion surface contact. Measurement of critical voltages have been applied to give information about various features of crystals. Variation of critical voltage with temperature can give accurate values of low angle scattering factors and Debye temperatures (Fisher and Shirley 1981). In alloys the presence of short and long range order can be revealed (Fisher and Shirley 1981) and changes in electronic charge distribution due to alloying can be detected (Shirley and Fisher 1979). In the present work, measurement of the [111] zone axis critical voltage is used to determine composition in the technologically important alloy system CdxHg1−xTe (CMT). Growth of CMT by liquid phase epitaxy (LPE) and metal organic vapour phase epitaxy (MOVPE) can lead to compositional non-uniformity (Raccah et al 1986). In assessing such growth it is important to be able to determine compositional variation on a sub-micron scale. Infra-red absorption measurements can give a macroscopic average composition. Cathodoluminescence has spatial resolution limited by carrier diffusion lengths. Only elastic electrons contribute to convergent beam electron diffraction (CBED), giving an effective probe size smaller than in energy dispersive X-ray microanalysis (EDX). Britton and Stobbs (1987) studied crossovers of deficit lines in the central disc of CBED patterns and concluded they were unsuitable for compositional determination, at least in GaAlAs. The use of measurements of the [111] zone axis critical voltage (ZACV) is shown here to be a useful technique for CdxHg1−xTe.
Light Sources
Published in Toru Yoshizawa, Handbook of Optical Metrology, 2015
Cathodoluminescence is the emission of light after excitation by impact of high-energy electrons. The impingement of energetic electrons generated by a cathode-ray tube, like in the case of a TV screen or an image intensifier (used in night vision devices), onto a luminescent material (phosphor or a semiconductor) results in the promotion of electrons from the valence band into the conduction band, leaving behind a hole. The recombination of an electron and a hole can be radiative process with emission of a photon or non-radiative process with creation of a phonon. The energy (color) of the emitted photon and the probability that a photon will be emitted, not a phonon, depend on the material and its purity.
A refined U-Pb age for the Stockholm granite at Frescati, east-central Sweden
Published in GFF, 2019
The zircons in sample 90030 are typically somewhat rounded and turbid, sometimes with rust-coated surfaces, and hence not of very good quality. Reasonably well-shaped and not so turbid zircon crystals were selected by handpicking from the non-magnetic 74–106 µm size fraction of this sample, one of the fractions used previously for the multigrain ID-TIMS dating. The selected zircon grains were mounted in epoxy and polished in half to reveal their inner structure. This structure was studied and documented both in reflected and transmitted light in a petrographic microscope, and in CL (cathodoluminescence) in a Philips scanning electron microscope. Subsequent to the SIMS analysis, the analyzed zircon crystals were imaged by BSE (back scatter electron) on a FEI Quanta 650 FEG scanning electron microscope.