Tayloring the Breakdown Voltage in High Electron Mobility Transistor: Theoretical and Experimental Results

In this paper the effect of a body contact to increase the breakdown voltage in GaAs based pseudomorphic HEMT has been theoretically investigated. The body contact is formed by a p-doped substrate connected to an ohmic back contact. By using a Monte Carlo simulation we show that the body contact reduces the density of holes generated by impact ionization and prevents holes from accumulating in the channel. ‘The breakdown effect is quenched as the density of acceptors in the substrate increases. This extends the range of the usable drain voltages

Stability of electrochemically prepared polyaniline films in aqueous and organic solutions.

Electroactive polyaniline films have been grown by galvanostatic, potentiostatic and cyclic voltammetry techniques in organic solutions based on LiClO4 or anilinium tetrafluoborate as salts and acetonitrile or acetonitrile/nitromethane mixtures as solvents. After storage of these films in a 1 M H2SO4, Na2SO4 aqueous solution, their stability was tested by cyclic voltammetry and impedance spectroscopy in this solution. Different levels of retention of the anodic charge have been found depending on the electrochemical technique and preparation solution. The impedance tests have revealed limited changes in the charge transfer resistance upon storage. This has been interpreted on the basis of a limited deactivation of the films, which in some cases would instead experience physical changes. Confirmation of this assumption was obtained via an SEM experiment. Films prepared by cyclic voltammetry in the above acidic solution and stored in acetonitrile-or propylene-carbonate-based electrolytes show major degradation processes, as evidenced by the appearance of quinone-like compounds and the marked increase in the charge transfer resistance. Finally, films prepared by different electrochemical techniques in acetonitrile-based solutions and stored in LiClO4-acetonitrile reveal moderate degradation phenomena

(Mo0.3V0.7)2O5 as a solid solution cathode for Li cells. Part. I°. Electrochemical behaviour of primary cells.

A new cathode material for Li cells has been prepared by using the Mo-rich limit of a range of solid solutions obtained by Mo substitution for V in V2O5. (Mo0.3V0.7)2O5 proves to possess two of the key requirements for cathodes to be used in Li cells, i.e., high specific capacity and rate capability. At 1.0 mA/cm2 and to 1.8 V cut-off it may incorporate 2.3 Li+/mole, thus giving capacities of ‚ 0.3 A h/g. At current drains higher than 5 mA/cm2, a substantial amount of this capacity may still be drawn. Low particle size (10-9 cm2/s) provide the basis for this rate capability. A comparison with the parent oxide, V2O5, shows that a higher energy density is obtainable with (Mo0.3V0.7)2O5

Nonaqueous Batteries with BiF3 Cathodes

Li cells based on BiF3 cathodes have been tested. In particular, the effect ofcathode formulation and compacting pressure, nature of the solution, temperature,and current density have been evaluated. Through x-ray analysis, cyclicvoltammetry, and coulometric analysis it was possible to ascertain that BiF3is reduced to Bi and then to Li3Bi. During the first reduction process, ternaryphases of the LixBiF3 type are probably formed. Li/BiF3 cells can give practicalenergy densities in excess of 200 W-hr/kg at the rate of 0.5 mA/cm

Non-stoichiometric molybdenum oxides as cathodes for lithium cells: Part IV. Factors influencing the performance of Li/Mo8O23 batteries

Mo8O23 was further investigated as a cathode material suitable for secondary Li batteries. Within the channels present in the basic slabs of its ReO3-type structure, it can accept up to 1.0 Li+/Mo through an octahedrical coordination of Li+ by O. The oxide performance in primary cells was seen to be largely dependent on cathode formulation and solution volume. As a secondary cathode it give single-cycle recharge efficiencies as high as 95% at 1.0 mA cm−2 and 0.5 e/Mo. Prolonged cycling in button cells at 1.0 and 2.0 mA cm−2 also gives satisfactory results. X-ray analysis shows that after cycling the structure does not suffer from significant distortion