Evaluation of capacitance-voltage spectroscopy by correlation with minority carrier lifetime measurements of PECV-deposited intrinsic amorphous layers

Abstract

Thick (150 nm) hydrogenated intrinsic amorphous silicon ((i) a-Si:H) layers, which are deposited with different recipes on crystalline silicon (c-Si) by plasma enhanced chemical vapour deposition (PECVD) are investigated by minority carrier lifetime measurements (eff) and capacitance-voltage C(V) spectroscopy during thermal treatment. The minority carrier lifetime measurements permit an evaluation of the surface passivation and thus the saturation of defects like dangling bonds at the (i) a-Si:H/c-Si interface. The capacitance difference between high and low frequency curves is a measure for the combination of the defects in the (i) a-Si:H bulk as well as at the (i) a-Si:H/c-Si interface. An evaluation of the sensitivity of the C(V) measurement is carried out by correlating these with minority carrier lifetime measurements during thermal treatment. The results of the measurements suggest that a direct correlation between the quality of defect passivation at the interface and in the bulk is not possible. The contribution of the interface defects to the difference in capacity is smaller than the resolution of the C(V) measurement. Imperfections in the structure of the (i) a-Si:H layer probably microvoids affect the bulk defects and the resulting differences in capacity more than changes at the (i) a-Si:H/c-Si interface. An investigation of the Si-H2 content by FTIR measurements supports this suggestion because the content indicates the formation of microvoids.