Experimental evidence for the annealing of surface defects in a-Si:H during deposition

The modulated photocurrent technique performed under different illumination conditions is used to derive a spatial spectroscopy of the defect distribution in hydrogenated amorphous silicon. The results show conclusive evidence for a defect density profile extending from the a-Si:H/air interface toward the bulk in samples deposited by rf glow discharge under standard conditions at low substrate temperature (373 K). This spatial inhomogeneity in defect density almost completely disappears after annealing at 473 K and also seems absent if the material is deposited at higher temperature (523 K). These results are supported by a model in which the surface defects, buried during a-Si:H deposition, are annealed out in a thermally activated process.