Injection Dependent Emitter Saturation Current Density Measurement under Metallized Areas Using Photoconductance Decay

We propose a novel method for the extraction of recombination characteristics of metal contacts on semiconductor substrates. We demonstrate this method for saturation current density measurements of contacts on boron doped emitters. It is easily generalized for the characterization of metallized high-low junctions, or of metal layers in direct contact with the bulk semiconductor. Our method is based on effective lifetime measurements as a function of metal contact area fraction. Under high injection conditions, saturation current densities of metallized junctions are extracted from the slope of the saturation current density as a function of metal coverage. At arbitrary injection levels, the difference between the saturation current density at metallized junctions and the saturation current density at passivated junctions is extracted from the slope of inverse effective lifetime versus metal contact fraction. If bulk recombination is negligible compared to emitter recombination, saturation current densities at the Simetal and at the passivated silicon surface can be independently determined for arbitrary injection levels. Our method is applied to saturation current density extraction for Al contacts on diffused boron emitters. Also, saturation currents at the emitter-air interface are extracted and compared to saturation current densities at the emitter-metal interface.