Electron microscopy analysis of silicon islands and line structures formed on screen-printed Al-doped p+-surfaces

Islands and line networks of aluminum-doped p⁺ regions formed in a conventional screen-printing process are investigated by a combination of different techniques. To characterize the microscopic nature of the islands (lateral dimensions 1–3 μm) and line networks of self-assembled nanostructures (lateral dimension ≤ 50 nm) advanced transmission electron microscopy (TEM), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray analysis (EDX) are combined. Aluminum inclusions are detected 50 nm below the surface of the islands and crystallographic aluminum precipitates of ≪ 7 nm in diameter are found within the bulk of the islands. In addition, aluminum inclusions (lateral dimension ∼30 nm) are found within the bulk of the self-assembled line networks. Our findings provide clear experimental evidence that the concentration peak generally measured at the surface of screen-printed Al-p⁺ regions is due to the microscopic structures formed on the silicon surface during the firing process.