Investigation of Gallium-Boron Spin-On Codoping for poly-Si/SiOx Passivating Contacts

A doping technique for p-type poly-Si/SiOx passivating contacts using a spin-on method for different mixtures of Ga and B glass solutions is presented. Effects of solution mixing ratios on the contact performance (implied open circuit voltage iV(oc), contact resistivity rho(c)) are investigated. For all as-annealed samples at different drive-in temperatures, increasing the percentage of Ga in the solution shows a decrement in iV(oc) (from similar to 680 to similar to 610 mV) and increment in rho(c) (from similar to 3 to similar to 800 m omega cm(2)). After a hydrogenation treatment by depositing a SiNx/AlOx stack followed by forming gas annealing, all samples show improved iVoc (similar to 700 mV with Ga-B co-doped, and similar to 720 mV with all Ga). Interestingly, when co-doping Ga with B, even a small amount of B in the mixing solution shows negative effects on the surface passivation. Active and total dopant profiles obtained by electrical capacitance voltage and secondary-ion mass spectrometry measurements, respectively, reveal a relatively low percentage of electrically-active Ga and B in the poly-Si and Si layers. These results help understand the different features of the two dopants: a low rho(c) with B, a good passivation with Ga, their degree of activation inside the poly-Si and Si layers, and the annealing effects.