Optical Properties of Amorphous Selenium Films
Amorphous selenium is essentially a glass, and all glasses exhibit some degree of structural relaxation effects during which the physical properties such as the refractive index and the bandgap change with time, called "aging". First of all, thermal annealing an a-Se film at T = 51?C for an hour reduces the thickness by ~15% and increases the refractive index by ~0.5%. The optical bandgap does not change by more than 0.2%. While the decrease in the thickness is thought to be due to the rearrangement of the molecular clusters and the amorphous network, the increase in the refractive index is believed to be linked to the densification and the polarizability of the material. Although the influence of the thickness of the film, the temperature of the glass substrate, and the doping of 67ppm of chlorine on the optical properties of the a-Se film was found to be negligible, there are noticeable changes during aging. It was found that an aged a-Se film that was cold deposited has an increased refractive index that is believed to be caused by densification alone. In a period of 2 months, the thickness of a cold deposited a-Se:67ppm-Cl film shrinks by 3.5% and the refractive index increases by 3.7%. The optical bandgap of the film decreases by 0.6%. Similar aging trends in the thickness, the refractive index, and the optical bandgap were also observed in a cold deposited a-Se film but no significant changes, at least not more than 0.5% deviation, were noted in a period of about 1-3 weeks in any aging a-Se films that were hot deposited or annealed.
Advisor:Johanson, Robert E.; Kasap, Safa O.
School:University of Saskatchewan
School Location:Canada - Saskatchewan
Source Type:Master's Thesis
Date of Publication:07/05/2006