Improved amorphous/crystalline silicon interface passivation with two-step intrinsic layers

Abstract

A novel way of two-step intrinsic (i) layers growth process was described to improve amorphous/crystalline silicon (a-Si:H/c-Si) interface passivation. This effort was guided by the study of the relationship between the bulk photoelectrical properties of a-Si:H film using a variable H₂-dilution gas flow ratio R = [H₂/SiH₄] and the passivation results of the amorphous/crystalline silicon interface. The results demonstrated that the a-Si:H/c-Si interface had more dominating influence on passivation than the bulk of a-Si:H films. However, when no epitaxial growth occurred on the a-Si:H/c-Si interface, the bulk quality of the a-Si:H film had a significant effect on passivation. The optimum two-step process was designed as follows: the initial stage of the i-layer was deposited at a lower R than the bulk to ensure that the interface remained within the amorphous phase and the second stage involved deposition using the optimum bulk a-Si:H film process to obtain the best quality of the passivated film. Although only a 5 nm thick passivated film was deposited on the polished Cz-Si wafers, the optimum effective lifetime was up to 1.7 ms. After annealing, the effective lifetime could be further increased to 2.5 ms and the corresponding implied V_oc was up to 0.724 V.