A comprehensive model for the electron mobility in wurtzite (hexagonal) GaN is developed. A large number of experimental mobility data and the results of Monte Carlo transport simulations reported in the literature have been evaluated and serve as the basis for the model development. The proposed model describes the dependence of the mobility on carrier concentration, temperature, and electric field. Good agreement between the modeled low-field mobility and measured data at both room and elevated temperatures has been obtained. The Monte Carlo results of the high-field transport are correctly reproduced by the model. The model can be easily incorporated into numerical device simulators.

An electron mobility model for wurtzite GaN

The individual effects of 15 impurities and their interaction with glue on zinc electrowinning from industrial acid sulphate electrolyte were characterized in terms of deposit morphology and preferred deposit orientation and in terms of current efficiency and zinc deposition polarization behaviour. The current efficiency decreased in a cyclical manner with increasing atomic number of the impurity element in each period of the periodic table. This decrease in current efficiency can be correlated to a corresponding increase in the rate of hydrogen evolution on the impurity metal. The various impurities produced four distinct zinc deposit morphologies and orientations and also produced characteristic changes in the cyclic voltammograms for the zinc deposition.

Characterization of impurity effects in zinc electrowinning from industrial acid sulphate electrolyte

Electron-spin-resonance (ESR) measurements have been performed on a series of wurtzite GaN films grown on sapphire substrates by low-pressure metal-organic chemical-vapor deposition. The sample set included films grown with both AlN and GaN buffer layers. The ESR signal results from residual donors with ${\mathit{g}}_{\mathrm{\ensuremath{\parallel}}}$=1.9510 and ${\mathit{g}}_{\mathrm{\ensuremath{\perp}}}$=1.9483. The g value and the effective mass can be explained using a five-band k\ensuremath{\cdot}p model. Nuclear hyperfine interactions are observed as a shift in the central resonance position, due to the Overhauser effect from which the density of the wave function at the Ga nucleus is derived. The ESR lines all have quite a sharp Lorentzian shape due to motional narrowing. At low temperatures (T20 K) the linewidth narrows with increasing temperature, consistent with electrons hopping from donor site to donor site. At higher temperatures the line broadens due to electron-phonon interactions. The concentration of uncompensated donors is independent of film thickness for GaN buffered films but increases monotonically with thickness for AlN buffered films, probably due to a decrease in the concentration of compensating centers. Photoluminescence measurements indicate that only the thickest films are homogeneous along the growth direction.

Electron-spin-resonance studies of donors in wurtzite GaN.

Results are reported of an experimental investigation of the effects of aqueous zinc(II) and sulfuric acid concentrations on current efficiencies and deposit morphologies of metallic zinc, aimed at designing a process for zinc recovery from solid industrial wastes by leaching and electrodeposition. Voltammetry and chronopotentiometry of additive-free solutions of zinc(II) sulfate and sulfuric acid were used to determine the zinc(II) reduction kinetics, prior to investigating the deposition in a Hull cell to observe the effects of the current density and the bath composition on current efficiencies and deposit morphologies. For a current density of 45 mA cm−2, best performance was obtained with zinc(II) concentrations of the same order of magnitude as the H+ concentration; too acidic solutions resulted in lower current yields and pronounced 3-D growth of the deposit.

Investigation of optimal conditions for zinc electrowinning from aqueous sulfuric acid electrolytes

Effect of Mn2+ ions on the electrodeposition of zinc from acidic sulphate solutions

Scientific research as a career.

Note on the Calibration of Conductivity Apparatus

Cobalt is present in minor amount in the circuit liquors of the Electrolytic Zinc Company's plant at Risdon, Tasmania. Despite the low concentration, cobalt would have profound effects on electrodeposition were steps not taken to minimize them. Some work done many years ago is now described in which an attempt was made to isolate the effects of the cobalt from those of other interfering elements. The properties of highly purified acidified zinc sulphate solutions were first examined. In such solutions there is no decrease of current efficiency (C.E.) with time. Its dependence on solution composition is shown to be governed by a distribution law. In the presence of cobalt the initial value of the C.E. is unchanged but it falls away, sometimes very rapidly, with time. Temperature, current density and colloid additions influence the rate of deterioration. The principles-governing this rate of fall are considered: a compound interest law is followed, with two constants, whose significance is discussed. Cobalt compounds are deposited as a thin film on the lead anode, lowering the anode overvoltage. Such anodes become passive when out of use. The anode effects are considered in relation to deposition of zinc. So also are changes in the ionic condition of the cobalt, which seem to be complex.

Influence of cobalt in the electrodeposition of zinc

An Accurate Form of Copper Coulometer

In the electrodeposition of zinc from acidified zinc sulphate solutions the loss in current efficiency (CE) due to evolution of hydrogen at the cathode has often been attributed to the presence of metal impurities, and it has been thought that in a pure solution the CE would be 100%. In this paper it is argued that, whatever the degree of purity achieved, hydrogen must always be produced simultaneously with zinc. At the start of electrolysis the CE is determined solely by the zinc/acid ratio, but when impurities are present the CE falls progressively as electrodeposition proceeds. Further, colloid silica which is always present in plant solutions is not responsible for the CE falling below 100%, nor are the lead anodes that are used in practice. Some effects of manganese, both at the anode and the cathode, are reported. The deleterious influences of cobalt and manganese together are also discussed.

The electrodeposition of zinc from acidified zinc sulphate solution

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