Control of bulk and interface properties in the fabrication of hydrogenated amorphous silicon films and structures by plasma CVD

The investigation in this thesis adopts an experimental approach towards the engineering of each layer in hydrogenated amorphous silicon (a-Si:H) structures. Material issues related to fabrication and processing have been addressed in order to control the properties of both intrinsic and doped a-Si:H. A multi-chamber plasma CVD system was developed for this purpose which has been used to fabricate materials under different deposition conditions. This establishes a correlation between materials processing and the properties of a-Si:H thin films. In particular, the deposition temperature is used to change the hydrogen content over a wide range and film properties are correlated with the monohydride and dihydride contents of the material and also with other temperature-dependent parameters. Characterization of the sensitivity of the optoelectronic properties of each layer to the deposition conditions is done with the intention of engineering the characteristics of a-Si:H devices. The effects of bulk material and interfaces at the contacts are also studied using Schottky barrier structures. Controlled changes are created at the metal/intrinsic and intrinsic/doped interfaces which are characterized using current-voltage response and spectral response of photogenerated carrier-collection. The transport simulation program AMPS is used to extract the material parameters and to gain insight into these interface phenomena. As a result, the importance of "in-situ" device fabrication is established.