Deep-level transient spectroscopy of Al/a-Si:H/c-Si structures for heterojunction solar cell applications

Abstract

A Deep-Level Transient Spectroscopy study is performed on Metal-Insulator-Semiconductor capacitors with a 70 nm amorphous silicon (a-Si:H) passivation layer, in order to study the electrically active defects present at the n- or p-type crystalline silicon (c-Si)/a-Si:H heterojunction. Trap filling kinetics identify two types of traps, namely, Pb0 dangling bond centers at the Si(100) interface and similar D centers in the a-Si:H, which are in close proximity to the interface and giving rise to a dominant peak around silicon midgap. The distinction between both kinds of deep levels is based on the carrier capture behavior, which is more point-defect-like for the Pb0 centers and varies according to the logarithm of the voltage pulse duration for the D defects, indicating capture of majority carriers from the substrate by tunneling into a-Si:H, the densities of which are correlated with capacitance-voltage measurements. This directly demonstrates that the recombination properties of the c-Si/a-Si:H interface are both determined by Pb0 and D defect states.