Growth characteristics of vacuum coated thick a-Se films for device applications

There has been a resurgence of interest in the growth characteristics of amorphous Se (a-Se) films due to their recently commercialized applications in x-ray imaging as x-ray photoconductors. Electronic quality a-Se films require the substrate temperature during vacuum deposition to be as high as possible but increasing the substrate temperature leads to amorphous films containing crystalline inclusions and eventually to polycrystalline films which have high conductivity and are therefore not useful as photoconductors. We prepared a variety of thick a-Se films on Al substrates by conventional vacuum deposition in which only the substrate temperature Tsb and boat temperature Tbt were varied. Experiments indicated the appearance of crystalline zones (crystallites) in the amorphous Se film as the substrate temperature was increased. We identified an experimental critical Tbt−Tsb boundary between amorphous films with and without crystalline inclusions. A model has been developed for the critical relationship ...