317 research outputs found
Phonon-limited carrier mobilities and Hall factors in 4H-SiC from first principles
Charge carrier mobility is at the core of semiconductor materials and devices
optimization, and Hall measurement is one of the most important techniques for
its characterization. The Hall factor, defined as the ratio between Hall and
drift mobilities, is of particular importance. Here we study the effect of
anisotropy by computing the drift and Hall mobility tensors of a
technologically important wide-band-gap semiconductor, 4H-silicon carbide
(4H-SiC) from first principles. With electronic structure and \textit{ab
initio} electron-phonon interactions, we solve the Boltzmann transport equation
without fitting parameters. The calculated electron and hole mobilities agree
with experimental data. The electron Hall factor strongly depends on the
direction of external magnetic field , and the hole Hall factor
exhibits different temperature dependency for and
. We explain this by the different equienergy surface shape
arising from the anisotropic and non-parabolic band structure, together with
the energy-dependent electron-phonon scattering.Comment: 24 pages, 8 figure
Shape and phase control of CdS nanocrystals using cationic surfactant in noninjection synthesis
Monodispersed CdS nanocrystals with controllable shape and phase have been successfully synthesized in this study by adding cationic surfactant in noninjection synthesis system. With the increase of the amount of cetyltrimethylammonium chloride (CTAC) added, the shape of the CdS nanocrystals changed from spherical to multi-armed, and the phase changed from zinc-blende to wurtzite. It was found that halide ion Cl- plays a key role in the transformation, and other halide ions such as Br- can also induce similar transformation. We proposed that the strong binding between Cd2+ and halide ions reduced the reactivity of the precursors, decreased the nuclei formed in the nucleation stage, and led to the high concentration of precursor in the growth stage, resulting in the increase of size and phase transformation of CdS nanocrystals. In addition, it was found that the multi-armed CdS nanocrystals lost quantum confinement effect because of the increase of the size with the increase of the concentration of CTAC
Iron-boron pair dissociation in silicon under strong illumination
The dissociation of iron-boron pairs (FeB) in Czochralski silicon under strong illumination was investigated. It is found that the dissociation process shows a double exponential dependence on time. The first fast process is suggested to be caused by a positive Fe in FeB capturing two electrons and diffusion triggered by the electron-phonon interactions, while the second slow one would involve the capturing of one electron followed by temperature dependent dissociation with an activation energy of (0.21 +/- 0.03) eV. The results are important for understanding and controlling the behavior of FeB in concentrator solar cells
Ghost city extraction and rate estimation in China based on NPP-VIIRS night-time light data
The ghost city phenomenon is a serious problem resulting from the rapid urbanization
process in China. Estimation of the ghost city rate (GCR) can provide information about vacant
dwellings. This paper developed a methodology to quantitatively evaluate GCR values at the
national scale using multi-resource remote sensing data. The Suomi National Polar-Orbiting
PartnershipâVisible Infrared Imaging Radiometer (NPP-VIIRS) night-time light data and moderate
resolution imaging spectroradiometer (MODIS) land cover data were used in the evaluation of the
GCR values in China. The average ghost city rate (AGCR) was 35.1% in China in 2013. Shanghai had
the smallest AGCR of 21.7%, while Jilin has the largest AGCR of 47.27%. There is a significant
negative correlation between both the provincial AGCR and the per capita disposable income of urban
households (R
Synthesis of hexagonal structured wurtzite and chalcopyrite CuInS2 via a simple solution route
Wurtzite semiconductor CuInS2 [CIS] has been reported in recent years. As a kind of metastable structure, it is a great challenge to synthesize pure wurtzite CIS at low temperature. In this paper, via a simple and quick solution route, we synthesize both wurtzite- and chalcopyrite-structure CIS. Well-controlled wurtzite CIS hexagonal plates are obtained when an appropriate agent is added. The influence of the used agent triethanolamine [TEA] has also been studied, and it turns out that without TEA, chalcopyrite CIS with a kind of rare morphology is formed through this method
Density functional theory study on the B doping and B/P codoping of Si nanocrystals embedded in SiO2
Doping silicon nanocrystals (Si NCs) embedded in silicon dioxide (SiO2) with boron (B) and phosphorus (P) is a promising way of tuning the properties of Si NCs. Here we take advantage of density functional theory to investigate the dependence of the structural and electronic properties of Si NCs embedded in SiO2 on the doping of B and P. The locations and energy-level schemes are examined for singularly B-doped or B/P-codoped Si NCs embedded in SiO2 with a perfect or defective Si/SiO2 interface at which a Si dangling bond exists. A dangling bond plays an important role in the doping of Si NCs with B or B/P. The doping behavior of B in Si NCs embedded in SiO2 vastly differs from that of P. The electronic structure of a B/P-codoped Si NC largely depends on the distribution of the dopants in the NC
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