Modeling current-voltage behaviour in oxide TFTs combining trap-limited conduction with percolation

Current-voltage behaviour of oxide TFTs is modeled based on trap-limited conduction and percolation theories. The mobility has a power-law dependence, in which percolation controls the exponent while trap states determine constant term in the power law. The proposed model, which is fully physically-based, provides a good agreement with measured transistor characteristics as well as transient operations of fabricated pixel test circuits for oxide-based OLED displays. © 2013 Society for Information Display.

Fourier spectrum based extraction of an equivalent trap state density in indium gallium zinc oxide transistors

Segregating the dynamics of gate bias induced threshold voltage shift, and in particular, charge trapping in thin film transistors (TFTs) based on time constants provides insight into the different mechanisms underlying TFTs instability. In this Letter we develop a representation of the time constants and model the magnitude of charge trapped in the form of an equivalent density of created trap states. This representation is extracted from the Fourier spectrum of the dynamics of charge trapping. Using amorphous In-Ga-Zn-O TFTs as an example, the charge trapping was modeled within an energy range of ΔEt 0.3 eV and with a density of state distribution as Dt(Et-j)=Dt0exp(-ΔEt/ kT)with Dt0 = 5.02 × 1011 cm-2 eV-1. Such a model is useful for developing simulation tools for circuit design. © 2014 AIP Publishing LLC.

Photosynthetic responses to inorganic carbon in Ulva lactuca under aquatic and aerial states

Intertidal macroalgae experience continual alternation of photosynthesis between aquatic state at high tide and aerial state at low tide. The comparative photosynthetic responses to inorganic carbon were investigated in the common intertidal macroalga Ulva lactuca L. along the coast of Shantou between aquatic and aerial state. The inorganic carbon dissolved in seawater at present could fully (at 10 degreesC or 20 degreesC) or nearly (at 30 degreesC) saturate the aquatic photosynthesis of U. lactuca. However, the aerial photosynthesis was limited by current ambient atmospheric CO2 level, and such a limitation was more severe at higher temperature (20degrees - 30degrees T) than at lower temperature (10 T). The carbon-saturated maximal photosynthesis of U. lactuca under aerial state was much greater than that under aquatic state at 10 degreesC and 20 degreesC, while the maximal photosynthesis under both states was similar at 30 degreesC. The aerial values of K-m (CO2) for photosynthesis were higher than the aquatic values. On the contrary, the values of apparent photosynthetic CO2 conductance under aerial state were considerably lower than that under aquatic state. It was concluded that the increase of atmospheric CO2 would enhance the primary productivity of U. lactuca through stimulating the photosynthesis under aerial state during low tide.

Effect of thermal annealing on hole trap levels in Mg-doped GaN grown by metalorganic vapor phase epitaxy

Deep trap levels in a Mg-doped GaN grown by metalorganic vapor phase epitaxy are studied with deep level transient spectroscopy (DLTS). The Mg concentration of the sample was 4.8 x 10(19) cm(-3), but the hole concentration was as low as 1.3x10(17) cm-3 at room temperature. The DLTS spectrum has a dominant peak D-1 with an activation energy of 0.41+/-0.05 eV, accompanied by two additional peaks with activation energies of 0.49+/-0.09 eV (D-2) and 0.59+/-0.05 eV (D-3). It was found that the dominant peak D-1 consists of five peaks, each of which has different activation energy and capture cross section. In order to investigate these deep levels further, we performed heat treatment on the same samples to observe the variations of activation energy, capture cross section, and amplitude of DLTS signals. It was found that the longer the heat treatment duration is, the lower the amplitude of DLTS peaks become. This suggests that the decrease of the DLTS signal originates from hydrogen atom outgoing from the film during the annealing process. The possible originality of multiple trap levels was discussed in terms of the Mg-N-H complex. (C) 2000 American Vacuum Society. [S0734-2101(00)01701-2].

Hole trap levels in Mg-doped GaN grown by metalorganic vapor phase epitaxy

Hole trap levels in a Mg-doped GaN grown by metalorganic vapor phase epitaxy (MOVPE) are studied with deep level transient spectroscopy (DLTS). The Mg concentration of the sample was 4.8 x 10(19) cm(-3), but the hole concentration was as low as 1.3 x 10(17) cm(-3) at room temperature. The DLTS spectrum has a dominant peak D-1 with activation energy of 0.41+/-0.05 eV, accompanied by two additional peaks with activation energies of 0.49+/-0.09 eV (D-2) and 0.59+/-0.05 eV (D-3). It was found that the dominant peak D-1 consists of five peaks, each of which has different activation energy and capture cross section. A relevant model for these levels is presented in relation to the Mg-N-H complexes. (C) 1998 American Institute of Physics. [S0003-6951(98)04340-X].

Optimization of biodiesel production from trap grease via acid catalysis

As a kind of waste collected from restaurants, trap grease is a chemically challenging feedstock for biodiesel production for its high free fatty acid (FFA) content. A central composite design was used to evaluate the effect of methanol quantity, acid concentration and reaction time on the synthesis of biodiesel from the trap grease with 50% free fatty acid, while the reaction temperature was selected at 95 degrees C. Using response surface methodology, a quadratic polynomial equation was obtained for ester content by multiple regression analysis. Verification experiments confirmed the validity of the predicted model. To achieve the highest ester content of crude biodiesel (89.67%), the critical values of the three variables were 35.00 (methanol-to-oil molar ratio), 11.27 wt% (catalyst concentration based on trap grease) and 4.59 h (reaction time). The crude biodiesel could be purified by a second distillation to meet the requirement of biodiesel specification of Korea.

Simulation of the Lanzhou Penning Trap LPT

The LPT (Lanzhou Penning Trap) is under construction and its task is to perforin direct mass measurement of fusion-evaporation residue, and if possible for heavy isotopes. Detailed simulations have been clone for a good understanding to the ion's movement and mechanics in the trap. The optimizal ion of the LPT is also performed based on the simulation. With a scale of 0.5 mm per grid used in the, simulation and many other limitations a highest mass resolution has been achieved to be 1.9 x 10(-5). An unexpected behavioin in the simulation related to magnetron motion has been found.

Penning trap mass measurements on nobelium isotopes

The Penning trap mass spectrometer SHIPTRAP at GSI Darmstadt allows accurate mass measurements of radionuclides, produced in fusion-evaporation reactions and separated by the velocity filter SHIP from the primary beam. Recently, the masses of the three nobelium isotopes No252-254 were determined. These are the first direct mass measurements of transuranium elements, which provide new anchor points in this region. The heavy nuclides were produced in cold-fusion reactions by irradiating a PbS target with a Ca-48 beam, resulting in production rates of the nuclei of interest of about one atom per second. In combination with data from decay spectroscopy our results are used to perform a new atomic-mass evaluation in this region.