Structural characterisation of hydrogenated a-Si using slow positron beam techniques

Hydrogenated amorphous silicon (a-Si:H) grown by hot wire chemical vapour d eposition is a promising candidate for robust inexpensive solar cells. Howe ver, prolonged exposure to light is known to lead to a reduction in efficie ncy of a-Si:H devices. The causes for this ageing effect are still unclear, but may be related to a structural relaxation or change in hydrogen conten t. In this work, results are presented for positron beam studies of the def ect structure, using both lifetime and Doppler-broadening spectroscopy, of a-Si:H grown under different conditions. (C) 2000 Published by Elsevier Sci ence B.V. All rights reserved.