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

Hydrogenated amorphous silicon (a-Si:H) grown by hot wire chemical vapour deposition is a promising candidate for robust inexpensive solar cells. However, prolonged exposure to light is known to lead to a reduction in efficiency 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 content. In this work, results are presented for positron beam studies of the defect structure, using both lifetime and Doppler-broadening spectroscopy, of a-Si:H grown under different conditions