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The authors compare resonant-phonon-assisted terahertz quantum-cascade lasers with different active region designs, i.e., one-well injector and three-well module, using an ensemble Monte Carlo method. Carrier transport under injection anticrossing, parasitic anticrossing, and collection anticrossing couplings are investigated for both structures. The results show that the main parasitic current channel is the resonance of the injector 1′ with the lower lasing level 3 and one-well injector design benefits a high injection selectivity because of a better Δ1′4/Δ1′3 ratio. Due to the diagonal radiative transition, the one-well injector design sacrifices the oscillator strength and modal gain to reduce the parasitic coupling. Temperature evaluation shows that longitudinal-optical phonon emission is the dominant scattering mechanism contributing to lasing and the calculated modal gain in the one-well design shows a slower decreasing rate with temperature. [ABSTRACT FROM AUTHOR]

Using the Wigner-Poisson transport model, we have theoretically investigated dynamical instability and transient behavior of a double barrier resonant tunneling device driven by a terahertz field. It is found that switching between different current states may be triggered by terahertz electromagnetic radiation. The transition between high- and low-current states could be explained by time-dependent energy-level coupling and nonlinear processes. The characteristic switching times correspond to the terahertz frequency range, suggesting that the system may potentially act as a terahertz switch. [ABSTRACT FROM AUTHOR]

Presents an analysis of electronic transport through GaAlAs barriers in gallium arsenide. Influence of the electric field on the apparent barrier height; Current voltage characteristics; Behavior of the GaAlAs barriers.

Presents a study which examined a series of unintentionally doped gallium aluminum arsenide epitaxial layers. Experimental conditions of the isolated interstitials; Analysis of the production of lithium interstitial donor states; Results from secondary-ion mass spectroscopy observations.

Characterizes uniformly silicon-doped aluminum arsenide layers and short-period gallium arsenide-aluminum arsenide superlattices grown in the same conditions by molecular beam epitaxy. Significance of superlattices based on gallium arsenide alloys; Characterization of aluminum arsenide layers; Discussion of electron-irradiation-induced defects.

A study of the structure and in-plane dielectric properties of BaZr0.2Ti0.8O3 thin film epitaxially grown on (LaAlO3)0.3(Sr2AlTaO6)0.35 (001) single-crystal substrates through pulsed-laser deposition has been carried out. X-ray diffraction measurements revealed a good crystallinity and tensile in-plane stress in the film. Fine grains with an average size of ∼20 nm were observed using atomic force microscopy. Curie temperature of the film was found to be ∼120 °C, which is 100 °C higher than that of the ceramic. Butterfly-shaped C-V curve confirmed the in-plane ferroelectric state in the film. A large dielectric tunability of ∼50% was found in the film. [ABSTRACT FROM AUTHOR]

There is a generally accepted view that there is an obvious distinction between proto‐porcelain and stamped stoneware. However, some early shards unearthed from the Dongtiaoxi region (northern Zhejiang) inspire people to rediscuss the relationship between them, because it is difficult to identify them as proto‐porcelain or stamped stoneware. In this work, we have collected samples from three of the earliest kiln sites (Piaoshan, Beijiashan and Nanshan) in the Dongtiaoxi region. We have analysed the chemical composition, firing temperature and phase composition of the samples. Comparing samples from the three kiln sites, we find that, from Piaoshan and Beijiashan to Nanshan, there has been progression in the manufacturing technology. The Shang proto‐porcelain and the stamped stoneware from Nanshan have similar raw materials, firing temperatures and body phase compositions—and they have obviously different decorative appearances, such as glazing or stamping. For ceramics from Piaoshan and Beijiashan, there is no clear distinction between glazed and unglazed samples. We believe that in the Dongtiaoxi region, the difference in the decoration between proto‐porcelain and stoneware became obvious up to the time of the Nanshan production but that, subsequently, two different paths for the development of high‐fired ceramics began to diverge. [ABSTRACT FROM AUTHOR]

A mass of Longquan porcelain shards carved with ' Guan' or the dragon patterns were unearthed in the early Ming Dynasty layer of the Fengdongyan kiln site at Dayao County. These celadon shards were fired in the Hongwu and Yongle eras of the Ming Dynasty. In order to research the raw materials and firing technology of the imperial porcelain, 85 typical shards were analysed by energy-dispersive X-ray fluorescence ( EDXRF). The results indicate that the contents of TiO2 and Fe2O3 in the body vary in the Hongwu and Yongle eras. Compared with Longquan glazes in the Southern Song Dynasty, the average values of K2O, Fe2O3 and TiO2 are higher, but that of CaO is lower in early Ming imperial porcelain glazes. Principal components analysis ( PCA) shows that different degrees of elutriation of the same raw materials are the main reason for this difference in the Hongwu and Yongle periods. However, the raw materials of imperial porcelain glazes show no obvious changes and have inherited the earlier tradition. The production and firing technology of imperial porcelain reached a higher level and had not declined in the Early Ming Dynasty. [ABSTRACT FROM AUTHOR]

Xiaoshan in Zhejiang Province was an important ceramic production area in ancient China. During recent years, local archaeologists have found a number of mound tombs dating to the Zhou Dynasty and the Spring and Autumn period. Many shards of stamped stoneware and proto-porcelain have been unearthed from these tombs. In this paper, we report how we collected ceramic shards from tombs and samples from local ancient kilns as reference materials in order to clarify their relationship. We have used the energy-dispersive X-ray fluorescence technique to analyse the chemical composition of the ceramic samples. The results indicate that some of the tomb artefacts may be imported from other production areas. We infer that the other tomb samples were produced at local kilns, but due to production process-related compositional differences, there are small differences in chemical composition between different categories of samples. [ABSTRACT FROM AUTHOR]