Effect of morphological structure on photosensitivity of chemically deposited PbS thin films

Publisher Website
Google Scholar
Abstract
Chemically deposited PbS thin films have been prepared for use as infrared detectors. A systematic and elaborate study using scanning electron microscopy shows that the structure and crystallite size are related to the photosensitivity. Both the role of chemical oxidant influencing the type of conductivity and morphological details such as crystallite size distribution have been investigated. It is observed that in the absence of oxidant the average size of crystallites is about 0.9 mu m. This decreases to 0.3 mu m for the concentration of oxidant imparting maximum photosensitivity and further reduces to 0.2 mu m or less at higher concentrations. A good photosensitive film is electronically p-type and has a more uniform crystallite size distribution with relatively loose compact structure. Annealing of the films at 393K under vacuum (5*10-2 Torr) for 4-5 h affects the electronic properties considerably but does not cause any appreciable change in the structure except in smoothing the grain boundaries to a certain extent. A qualitative explanation in terms of rate of chemical reaction is offered for the morphological parameters observed in these experiments. It is also suggested that the photocharacteristics could be viewed partly as a support for barrier modulation but having its origin in the physical nature of the films.