A Scanning Spreading Resistance Microscopy Study on a Laser-Doped Selective Phosphorous Emitters
In this work, we present scanning spreading resistance microscopy (SSRM) measurements of a phosphorous emitter formed via tube furnace diffusion and a laser-doped selective emitter (LDSE) processed by additionally doping the tube furnace diffused emitter. The nonlaser-doped emitter is found to be widely homogeneous along the alkaline textured silicon surface. In contrast, the LDSE features large fluctuations in doping depth, almost constant doping concentration along the (laser-modified) surface within a depth of <0.2 mm, and a steep drop of the doping concentration at the p-n-junction. In some parts of the LDSE, the local doping profile is found to decrease stepwise. These findings are new to the photovoltaic community since the named phenomena are not resolved by common characterization methods such as electrochemical capacitance-voltage (ECV) profiling. The limits of ECV profiling are demonstrated by simulating an ECV profile from an SSRM measurement. In this context, we introduce a new method to correct ECV measurements performed on rough surfaces.