The effect of emitter recombination on the effective lifetime of silicon wafers

The application of photoconductance measurements of the effective lifetime of silicon wafers to determine the saturation current density of diffused emitter regions is reviewed. To illustrate the technique, a sequence of experiments is presented with phosphorus diffusions of various types: oxide passivated and unpassivated, lightly doped and heavily doped. Different material qualities (FZ, CZ and multicrystalline silicon) are considered, as well as different substrate resistivities. The dependence of the effective minority carrier lifetime on injection level is discussed. The limitations imposed by emitter recombination on the measurable minority carrier lifetimes are clarified and demonstrated experimentally. This bound varies with the dopant density and thickness of the silicon wafer.