Photodegradataion and Stability of a-Si Prepared at High Deposition Rates

Abstract

ABSTRACTA-Si films with a constant optical band gap were prepared by plasma CVD from silane at deposition rates up to 17 Å/s under controllably varied conditons and characterized by a number of techniques. Photodegradation under AM1 simulator has been done for 50 hours and for 4–17 hours under 2 Watt/cm2 dye laser illumination at a wavelength corresponding to an absorption coefficient of about 104 cm-1 up to saturation. Samples with different initial value of σ(d) and σ(ph) show different rates of photodegra-dation, but they reach very similar saturation values. The fast photode-gradation with the dye laser is equivalent to a long term (several thousand hours) photodegradation under AM1. The AMI photodegradation for 50 to 100 hours does not yield any reliable measure of the stability of the films. The best films, which were prepared at a high deposition temperature show a low saturation defect density of about 5·1016 cm-3 (CPM-data).