No description available.

No description available.

No description available.

No description available.

No description available.

<p> The properties and device applications of silicon thin films vacuum evaporated both onto single crystal silicon and onto silicon dioxide substrates have been investigated. </p> <p> The feasibility of obtaining device quality homoepitaxial silicon thin films by vacuum evaporation onto non heat-treated substrates having temperatures of 700°C has been demonstrated. A new technique, that of gas-doping, has been developed and has been shown to be capable of reproducibly introducing controlled concentrations of doping impurities in the range applicable to device fabrication into the deposited layers. The combined deposition-doping technique has been employed in the production of silicon layers containing impurity steps more abrupt than may be obtained by conventional fabrication techniques. </p> <p> The electrical properties of the vacuum evaporated homoepitaxial silicon layers have been shown to be comparable in most respects to those of bulk high purity single crystal silicon. The characteristics of rectifying and of varactor diodes prepared by the technique of vacuum evaporation combined with gas doping have been considered. </p> <p> Silicon films evaporated onto Si02 substrates have been shown to possess structures ranging from amorphous through randomly oriented polycrystalline to oriented polycrystalline as the substrate temperature is increased from 25°C to 850°C. The electrical characteristics of doped polycrystalline films obtained both by vacuum evaporation combined with gas doping and by the diffusion-annealing of amorphous films have been shown to be comparable with those reported for similar material deposited by chemical techniques. The experimentally observed properties of the disordered material have been qualitatively explained employing an inhomogeneous film model. The suitability of thin films of doped polycrystalline silicon on sio2 substrates for the production of high value resistors for monolithic integrated circuits has been considered. </p> / Thesis / Doctor of Philosophy (PhD)

Amorphous Silicon(a-Si) films have attracted the attention of several investigators as it is an economical material for devices. One of the problems that is addressed is the doping of these films after they are prepared. In this thesis, we investigated the effects of doping amorphous Sil­icon films(prepared by r.f. sputtering) with Aluminium(Al) by ther­mal diffusion. Amorphous Silicon films have been prepared on glass substrates at optimal process parameters. Then, the a-Si films are coated with Al by vacuum evaporation and subjected to heating in N2 atmosphere in the temperature range 300°C to 600°C for different durations. After etching Al layer, it has been found that some of the films which are heated around 550°C contain filament like polycrystalline regions surrounding islands of a-Si. This structure has been confirmed through Scanning Electron Mi-croscope(SEM) photographs and electrical conductivity measurements. SEM photographs indicate that, bright regions of amorphous mate­rial are surrounded by dark regions of relatively higher conducting boundaries. The electrical conductivity study shows that there is sharp increase in conductivity of Al doped films, which is attributed to the conduct­ing polycrystalUne filament. A simple model has been proposed to explain the variation of con­ductivity of these transformed films, with process parameters and with temperature. Schottky barrier diodes have been fabricated using these trans­formed materials and their characteristics explained.