Determination of Acceptor Ratio and Iron Concentration in Co-doped Silicon

Low-cost photovoltaic grade feedstock using multiple dopants - mainly Boron and Phosphorous but also Gallium and trace amounts of Aluminum - is currently establishing itself on the market. In this paper, the measurement of dissolved iron by lifetime spectroscopy introduced on the incumbent Boron-only doped Silicon is adapted to materials with several acceptors. A detailed theoretical description is given and pitfalls are identified. Since precise knowledge of the relative acceptor concentrations is necessary for a correct iron determination, a novel method for measuring acceptor concentration fractions in Silicon is proposed. It uses lifetime spectra analysis to determine the crossover point position. Using this simple method, it is possible to fully analytically characterize compensated silicon doped with two acceptor types.