Pulsed Laser Melting of Semiconductors for Photovoltaics

Polycrystalline silicon (poly-Si) on SiOx passivating contacts are believed to be promising candidates for the development of new generation solar cells. The ultrathin layer of tunneling oxide located between the crystalline (c-Si) base and poly-Si emitter provides the passivation of the emitter by reducing the recombination rate. Hyperdoping of a poly-Si layer with Boron and Gallium and overcoming the solid solubility limit of dopants can enhance the conductive performance of a semiconductor. For this reason, nanosecond scale pulsed laser melting (PLM) of the poly-Si layer at different energy densities was used. Laser pulses induce melting and the subsequent recrystallization of the poly-Si layer, leading to the diffusion, incorporation and electrical activation of the dopant atoms, while preserving the quality of the tunneling oxide. The conductive properties of post-PLM samples were measured using Van-der-Pauw method, then the SIMS profiles of dopant distribution were analyzed. Finally, the device prototypes based on the B- and Ga-doped poly-Si layer were fabricated and tested. In addition, it was discovered that after using PLM on samples with a pyramid-textured poly- and amorphous Si surface, pinhole openings exactly at the tips of the pyramids are produced. Hence, the possibility of controlling the radius, location, and the pinhole density simultaneously using PLM was analyzed. To study pinhole conductivity, c-AFM measurements were conducted.