Influence of DC saddle-field discharge deposition parameters on the structure of hydrogenated amorphous carbon semiconductor

grantor: University of TorontoThin hydrogenated amorphous carbon (a-C:H) films were grown using an innovative deposition system, the DC saddle-field discharge. The properties of a-C:H films and the dependence of their properties on the growth conditions have been investigated. The study of deposition conditions has led to a better understanding of the deposition processes in the DC saddle-field discharge. This has ensured a greater degree of control of the properties of a-C:H films grown using the system, leading to the growth of a wide variety of films whose properties included those of a-C:H films described in literature. The basic DC saddle-field discharge mechanisms have been analysed with the help of a standard DC discharge model. The effect on the discharge conditions of the semitransparency of the electrodes has been characterized. When the DC saddle-field discharge is used as a deposition system for thin films such as hydrogenated amorphous carbon films, it has been shown that this deposition system allows for independent control of two parameters critical in the growth of thin films, the ion energy and the density of the ions reaching the substrate. In the DC saddle-field discharge, the range of combinations of the ion density and the energy of ions reaching the substrate is greatly extended, in comparison to the standard DC deposition system. The study of a-C:H film growth as a function of the energy and density of ions incident on the growing surface has led to an understanding of the a-C:H growth mechanisms and the parameters which influence these mechanisms. The presence of both sp3 and sp2 bonds in a-C:H is responsible for the wide range of properties of this material. However, this diversity of bonding configurations results in a complex interpretation of the electronic structure and the chemical bonding of a-C:H. The analysis of optical measurements performed on a set of a-C:H films has confirmed the model proposed by Robertson where the sp2 content controls the Tauc energy gap. However, a better understanding of the change in the structure of the films has now been reached. The change from wide band gap films (2.2 eV) to narrow band gap films (1.2 eV) is matched by an important structural change. Through this analysis, trends in the complex a-C:H bond distributions have been related to optical properties of the film. The important properties of a-C:H, such as Tauc energy gap and hydrogen content, have also been related to plasma behaviour through deposition parameters.Ph.D