Influence of deposition parameters on the optical absorption of amorphous silicon thin films

Amorphous silicon (aSi) is a promising material for application in mirror coatings with low thermal noise in future gravitational-wave detectors. However, the optical absorption of aSi is currently too high to meet the requirements of these instruments. Previously measured absorption values vary significantly for different deposition methods and postdeposition treatments. To investigate the absorption of aSi, we systematically varied key deposition parameters using pulsed laser deposition. Varying the deposition temperature resulted in a spread in mobility gap energy of the aSi; however, no clear correlation of temperature and mobility gap could be observed. Varying the pulse energy and repetition frequency altered the deposition rate of the coating and produced a correlated change in the absorption.