On the nature of emitter diffusion and screen-printing contact formation on nanostructured silicon surfaces

In this paper, we study the impact of change in emitter diffusion profiles on the electrical characteristics of nanotextured surfaces formed by an inline plasma-less dry-chemical etching process. Our experimental results and process simulations suggest that a deeper highly doped region and a significantly higher inactive P concentration in the emitter plays a determining role in defining recombination, as well as the resistive losses in nanotextured surfaces. Low emitter saturation current densities on phosphorous-diffused surfaces are achievable after passivation with either SiNx (j0e,m in ≈ 81 fA/cm2) or AlOx/SiNx (j0e,m in ≈ 31 fA/cm2) if the emitter recombination channels are suppressed. Based upon macroscopic measurement of contact resistivity and microscopic analysis of the contact areas, we propose that the formation of numerous metal-semiconductor direct contact points on the peak and the plateaus of the nanostructures are mainly responsible for a low specific contact resistivity (rc,m in ≈ 1.2 mO · cm2) achievable in these surfaces.