Impact of rapid thermal processing on bulk and surface recombination mechanisms in FZ silicon with fired passivating contacts

Abstract

We investigate bulk and interface recombination in crystalline silicon with p-type fired passivating contacts. These consist of a chemical oxide and an in-situ doped layer of SiCx with low carbon content. Following a rapid thermal annealing to activate the dopants in the SiCx layer, we observe the formation of bulk defect states close to one of the band edges at temperatures between 450 and 700 °C. At temperatures of 800 °C and above, these bulk defects are increasingly cured. At the same time, the surface passivation provided by the interfacial oxide is increasingly deteriorated at temperatures above 800 °C, eventually permitting the injection of a recombination current into the SiCx layer. Consequently, there is a trade-off for the effective minority carrier lifetime with an optimum between 800 and 830 °C. We develop a formalism that distinguishes recombination through shallow bulk defects from the recombination current at the surface in a plot of the effective lifetime τeff over the ratio n/p.