Defect Formation in Silicon During Laser Doping

Laser doping in industrial crystalline solar cells creates a selective emitter and thereby enhances the efficiency. Nevertheless, if not done carefully, the irradiation of the semiconductor introduces defects. We have suppressed defect formation by using a laser beam that is focused to a line with a width of only several micrometers. The maximal line width for a defect free recrystallization, however, depends on the surface orientation of the silicon. Using a transmission electron microscope, we find a dislocation-free recrystallized layer on (100)-oriented silicon wafers that are irradiated with a line focus smaller than or equal to 15 μm. For (111)-oriented surfaces, this holds for the use of a 5.2-μm-wide line focus. Wafers that are irradiated with a circular laser focus of diameter D = 36 μm show the formation of microcracks, but no hints of dislocations are found using transmission electron microscopy (TEM).