Structural and optical properties of amorphous germanium chalcogenide films prepared by PECVD

• Main Author: Sleeckx, Erik
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1996
• Subjects: Condensation; Condensed matter physics; Materials science
• ISBN: 0591072092; 9780591072099

This PhD consists of two parts: (1) the preparation by plasma-enhanced chemical vapour deposition (PECVD) and characterization of amorphous Ge-S-, Ge-Se- and Se-films (2) the study of irreversible and reversible changes in these films after annealing and illumination. The preparation of Ge-S films by PECVD was not very successful. The main problem was the incorporation of sulphur in the films. Ge-Se amorphous thin films on the other hand can easily be obtained by PECVD. The films prepared by PECVD exhibit a closer resemblance to glasses than to films prepared by thermal evaporation. Annealing and illumination of virgin films leads to changes in the optical bandgap caused by an increase of the density of the Ge-Se bonds, a decrease of the homopolar bond concentration (short range order) and the long range order. The changes in the films prepared by PECVD are more complex due to the presence of hydrogen in these films. Important factors in the photo-darkening phenomenon are the temperature at which the film is illuminated and the Se concentration in the film. We suppose that the process responsible for the photo-darkening is the same at room temperature, 77 and 13 K. The model we propose based on a study of Wong and co workers, gives a good explanation for the experimental results.