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 ρ 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 ∼680 to ∼610 mV) and increment in ρ c (from ∼3 to ∼800 mΩ cm 2 ). After a hydrogenation treatment by depositing a SiN x /AlO x stack followed by forming gas annealing, all samples show improved iVoc (∼700 mV with Ga‐B co‐doped, and ∼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 ρ c with B, a good passivation with Ga, their degree of activation inside the poly‐Si and Si layers, and the annealing effects.