Substrate temperature effect on the stability of hydrogenated amorphous silicon films deposited at high rates

The metastability of the electronic properties of hydrogenated amorphous silicon (a-Si:H) films deposited at high rates by the rf glow discharge decomposition of mixtures containing 40% silane in helium is compared with that of device quality a-Si:H material deposited at 250°C under standard low deposition rate conditions. The density of states above the Fermi level of the films obtained under helium dilution decreases for deposition temperatures increasing from 250 to 350°C, both after annealing and after light soaking. At 350°C, the density of states becomes comparable in both states to that of device quality low deposition rate a-Si:H. We observe a correlation between these results and the degradation of the photoconductivity and the below-Fermi-level defect density measured in situ during light soaking.