[en] The wet etching properties of a HfSiON high-k dielectric in HF-based solutions are investigated. HF-based solutions are the most promising wet chemistries for the removal of HfSiON, and etch selectivity of HF-based solutions can be improved by the addition of an acid and/or an alcohol to the HF solution. Due to densification during annealing, the etch rate of HfSiON annealed at 900 ⁰C for 30 s is significantly reduced compared with as-deposited HfSiON in HF-based solutions. After the HfSiON film has been completely removed by HF-based solutions, it is not possible to etch the interfacial layer and the etched surface does not have a hydrophobic nature, since N diffuses to the interface layer or Si substrate formation of Si-N bonds that dissolves very slowly in HF-based solutions. Existing Si-N bonds at the interface between the new high-k dielectric deposit and the Si substrate may degrade the carrier mobility due to Coulomb scattering. In addition, we show that N₂ plasma treatment before wet etching is not very effective in increasing the wet etch rate for a thin HfSiON film in our case. (semiconductor technology)

[en] A method is proposed, using a triac like structure, to measure the spreading velocity of the plasma in the ν layer. For a ν layer width of 150μm the spreading velocity is found to be equal to 100μm/μs

[en] Highlights: • Energy decomposition analysis elucidates the nature of P3HT backbone flexibility. • Weak $\pi$ conjugation in Br-P3HT is attributed to steric hindrance of bromo group. • The steric hindrance causes out-of-plane backbone torsion and spectral blue shift. • A torsional defect originating from bromination breaks the $\pi$ conjugation. In poly(3-hexylthiophene) (P3HT), it is suggested that bromination disturbs the $\pi$ conjugation and reduces the carrier mobility. To investigate the deconjugation mechanism, we theoretically studied a key flexibility of the Br-P3HT backbone, namely inter-ring SCCS dihedral torsion, in terms of potential energy curve, geometry-based aromaticity index, and decomposed energies of inter-monomer interaction. The linkage between bromination and the excitation energy was also investigated. We concluded that steric repulsion due to bulky bromo group can cause out-of-plane SCCS torsion of Br-P3HT and consequent shortening of the conjugation length, not electronic substituent effect, leads to blue shift of the $S_0\to S_1$ excitation energy.

[en] The problem of the spatial localization of free electrons in 4H-SiC metal—oxide—semiconductor field effect transistors (MOSFETS) with an accumulation- and inversion-type n channel is theoretically analyzed. The analysis demonstrates that, in optimally designed accumulation transistors (ACCUFETs), the average distance from the surface, at which free electrons are localized, may be an order of magnitude larger than that in inversion MOSFETs. This can make 4H-SiC ACCUFETs advantageous as regards the effective carrier mobility in a conducting channel.

[en] A computer analysis of the charge-transport process in an MOS transmission line (MOSTL) operating in deep depletion is presented. The mathematical model is developed taking into account time-dependent gate voltages, field-dependent surface mobility, and voltage-dependent depletion capacitance. A distributed equivalent circuit model is derived. The contributions of the physical transport mechanisms are investigated from the standpoint of assesing the influence of the design parameters and operating conditions on the performances of the structure. Several driving techniques which use time-varying gate voltages are proposed and simulated. Special emphasis is directed toward the possible improvements of the performances of an MOSTL used as a bit line in a continuously charge-coupled RAM or as a variable delay line for digital signals. To a certain extent, the theory derived in this paper is also valid for charge-transfer devices, in particular for the charge-transfer process in bucket-brigade devices and under the transfer gates of two-phase CCD's. (author)

[en] Electrical spin, which is the key element of spintronics, has been regarded as a powerful substitute for the electrical charge in the next generation of information technology, in which spin plays the role of the carrier of information and/or energy in a similar way to the electrical charge in electronics. Spin-transport phenomena in different materials are central topics of spintronics. Unlike electrical charge, spin transport does not depend on electron motion, particularly spin can be transported in insulators without accompanying Joule heating. Therefore, insulators are considered to be ideal materials for spin conductors, in which magnetic insulators are the most compelling systems. Recently, we experimentally studied and theoretically discussed spin transport in various antiferromagnetic systems and identified spin susceptibility and the Néel vector as the most important factors for spin transport in antiferromagnetic systems. Herein, we summarize our experimental results, physical nature, and puzzles unknown. Further challenges and potential applications are also discussed. (invited review)

[en] Researchers' mobility is significant for the quality of research, although mobility does not necessarily have an intrinsic value. Sweden appears to have a lover degree of mobility when compared to a selection of successful research countries. The Swedish Research Council shall, according to the instruction from the government , promote researcher mobility. This study explores job-mobility within the Swedish academic system based on register studies and draw some conclusions on the degree of mobility in different different disciplines, differences between men and women as well as on the development of comprehensive and easy to follow indicators for mobility. The study intends to provide support for recommendations on researcher mobility within the Research Council's overarching goal to promote excellence in research. (Author)

[en] This work presented theoretical studies on the one-dimensional (1D) nanowires constructed from fullerene C₂₀ cages based on first-principle calculations. The relative energies, electronic, charge transport, and mechanical properties of the 1D nanowires were investigated systemically and in detail. It is found that formations of the C₂₀ nanowires built from isolated cages were all energetically favorable. They also exhibit high kinetic stability according to molecular dynamics simulations. Although they were all constructed with C₂₀ cages as building blocks, NW-2-NW-6, and NW-9 are semiconductors, whereas NW-1, NW-7, and NW-8 exhibit metallic property. Thus the metallic/semiconducting properties of the 1D C₂₀ nanowires can be mainly determined by the connecting patterns. High charge mobility was revealed for the 1D C₂₀ nanowires based on the deformation potential theory and effective mass approach. Further understanding of the charge mobility is achieved with the aid of crystal orbital analyses. Moreover, the mechanical property of the 1D C₂₀ nanowires was also studied based on the results of Young's modulus. (author)

[en] Charge carrier mobility in disordered organic materials depends on the chemical potential. Chemical potential has an implicit functional dependence on the carrier concentration and the density of states. However, for efficient calculation of mobility in simulation programs it is highly useful to have an explicit and accurate approximation for the chemical potential. In this study, we focus on analytical approximation for the chemical potential in organic materials with Gaussian disorder and provide an accurate expression in both non-degenerate and degenerate regimes. (paper)

[en] Reaching device efficiencies that can rival those of polymer-fullerene Bulk Heterojunction (BHJ) solar cells (>10%) remains challenging with the “All-Small-Molecule” (All-SM) approach, in part because of (i) the morphological limitations that prevail in the absence of polymer and (ii) the difficulty to raise and balance out carrier mobilities across the active layer. In this paper, the authors show that blends of the SM donor DR3TBDTT (DR3) and the nonfullerene SM acceptor O-IDTBR are conducive to “All-SM” BHJ solar cells with high open-circuit voltages (V_OC) >1.1 V and PCEs as high as 6.4% (avg. 6.1%) when the active layers are subjected to a post-processing solvent vapor-annealing (SVA) step with dimethyl disulfide (DMDS). Combining electron energy loss spectroscopy (EELS) analyses and systematic carrier recombination examinations, the authors show that SVA treatments with DMDS play a determining role in improving charge transport and reducing non-geminate recombination for the DR3:O-IDTBR system. Finally, correlating the experimental results and device simulations, it is found that substantially higher BHJ solar cell efficiencies of >12% can be achieved if the IQE and carrier mobilities of the active layer are increased to >85% and >10^-4 cm² V^-1 s^-1, respectively, while suppressing the recombination rate constant k to <10^-12 cm³ s^-1.