We report on Hall transport measurements of two p-type Cd-doped InP epilayers and two Mg-doped InP layers with low compensation levels. The acceptor concentrations and the compensation ratios were determined with an extended-state Hall transport model, which provided a good description of the mobilities and the free-hole concentrations. Binding energies of 51 and 38.7 meV were measured for the purest Cdand Mg-doped samples, respectively. Nearest-neighbor hopping was present in all samples, consistent with a model by Shklovskii and Efros. Saturation of the corresponding conductivity was observed in the Mg-doped samples, in excellent agreement with a model by Shklovskii and Yanchev.Variable-range hopping was observed below 6 K, and was found to be consistent with Mott's expression for the conductivity. An unusual sign reversal of the Hall constant was observed in the Mg-doped samples at the onset of impurity conduction.

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We report on the electrical properties of Zn-doped (p-type) InP epilayers grown by metalorganic vapor-phase epitaxy. A detailed Hall transport model, accounting for the various scattering mechanisms in semiconductors and including valence-band degeneracy effects and inter- and intraband transitions, has been used for the analysis of the data. It provided excellent simultaneous agreement with the free-hole concentration and the mobility for Zn concentrations in the range of 7×1016–2×1018 cm−3. Those concentrations, for which the Hall factor was found close to 1, were confirmed by secondary-ion mass spectroscopy profiles. The binding energies of the samples were in the range of 42.7–26.2 meV and decreased with increasing Zn concentration. A simple approach, based on free-hole statistics, is proposed for the determination of the impurity concentrations of the lightly doped samples. An increased residual donor concentration, observed at a higher doping level, has been discussed.

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Transparent co-doped TiO 2 thin films have been fabricated by sol-gel dip-coating. The doping is achieved using low concentrations of neodymium (Nd), silver (Ag), and copper (Cu). A significant effect of doping is noticed on the morphology and optical properties of thin films. XRD analysis confirms the formation of a pure anatase phase with a deterioration of the crystallinity upon doping. The co-doped TiO 2 thin films present larger crystallite size compared to other films. The surface roughness revealed by AFM increases from 0.9 nm for pure TiO 2 up to 5 nm for doped thin films. UV-vis spectroscopy shows that the bandgap energy slightly decreased for co-doped Ag-Nd/TiO 2 and Cu-Nd/TiO 2 . Photocatalytic degradation of MB significantly decreases upon doping. A mechanism based on combined effects of doping, annealing and nature of substrate is proposed to explain the photodegradation behaviour.