The experimental data on the Hall measurements have been used to characterize deep electron trapping levels in Cr doped semi-insulating GaAs crystals. The energy of the level below the conduction band edge has been found to be ∼ 0·8 eV and is thought to be related to Ga vacancies in the host crystal and Cr impurities.

Highly transparent and highly conducting films of SnO₂:F were prepared by chemical vapour deposition technique. The films prepared at 350°C substrate temperature and 2·5 lit. min⁻¹ flow rate of oxygen showed maximum figure of merit. The optimum doping concentration of fluorine was 1·02 wt%. The Hall experiment showed that the films prepared at optimum conditions had high carrier concentration and high mobility.

High temperature superconducting films of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O have been deposited on different substrates using conventional techniques, like flash evaporation and spray pyrolysis. The microstructural investigation of the films by SEM technique reveals the partially oriented nature of the crystallites. In the case of spray-deposited Bi-Sr-Ca-Cu-O HTSC films it has been found that film/substrate mismatch is not the decisive factor for the superconducting transition temperatureT_c.