Laser assisted boron doping of silicon wafer solar cells using nanosecond and picosecond laser pulses

In this paper, laser-assisted boron doping of planar and textured silicon wafers is investigated and optimized. Two laser types - a ns laser and a ps laser - are used, both operating at 532 nm. The following laser parameters are varied: pulse energy, repetition rate and laser scribing speed. The boron sources are commercially available spin-on dopant sources. The ps laser gives not satisfactory sheet resistance results and is thus not suitable for creating heavily doped p-type layers using the laser doping approach. In contrast, the ns laser is able to controllably realize heavily doped p-type profiles with desired sheet resistance value of below 100 Ohms/square. On planar surfaces, we realize profiles with a depth of about 0.5-2 μm. Interestingly, on textured samples, the heavily doped profile is found to be much thicker (about 3-5 μm).