Electron microscopy analysis of crystalline silicon islands formed on screen-printed aluminum-doped p-type silicon surfaces

The origin of a not yet understood concentration peak, which is generally measured at the surface of aluminum-doped p(+) regions produced in a conventional screen-printing process is investigated. Our findings provide clear experimental evidence that the concentration peak is due to the microscopic structures formed at the silicon Surface during the firing process. To characterize the microscopic nature of the islands (lateral dimensions of 1-3 mu m) and line networks of self-assembled nanostructures (lateral dimension of <= 50 nm), transmission electron microscopy, scanning electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray analysis are combined. Aluminum inclusions are detected 50 nm below the surface of the islands and crystalline aluminum precipitates of <= 7 nm in diameter are found within the bulk of the islands. In addition, aluminum inclusions (lateral dimension of similar to 30 nm) are found within the bulk of the self-assembled line networks. (c) 2008 American Institute of Physics.