Simulation and characterization of epitaxial n- and p-type emitters on silicon wafer solar cells

Epitaxial emitters deposited by atmospheric pressure CVD have been studied using different characterization methods such as spreading resistance profiling (SRP) or electrochemical capacitance voltage profiling (ECV). Comparing simulations with measured data, very low minority carrier lifetimes of tau(eff) = 20 mu s have been determined for FZ-material after a standard epitaxy process. LBIC measurements showed very low and inhomogeneous distributed diffusion lengths in the range of 100-250 mu m before process optimization. Therefore an emitter epitaxy process working at lower temperatures was developed [1] leading to diffusion lengths of 750 mu m. The effective minority carrier lifetimes and emitter saturation currents were determined using QSSPC measurements. For samples with an emitter, deposited at optimized temperature, a best value for the effective minority carrier lifetime of tau(eff) = 212 mu s was measured and an emitter saturation current could be determined to J(0e) = 46 fA/cm(2). In order to investigate the stress in the epitaxial layers mu Raman and mu PL measurements were performed showing no increased values at the interface. The doping density in boron doped emitters was determined with mu PL and in good agreement with measured ECV-profiles. The Shockley-Read-Hall lifetime in the emitter bulk showed no increased values at the interface between substrate and epitaxial layer.