Investigation of Gallium–Boron Spin‐On Codoping for poly‐Si/SiO_x Passivating Contacts

Abstract

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 iVoc, contact resistivity ρc) are investigated. For all as‐annealed samples at different drive‐in temperatures, increasing the percentage of Ga in the solution shows a decrement in iVoc (from ∼680 to ∼610 mV) and increment in ρc (from ∼3 to ∼800 mΩ cm2). After a hydrogenation treatment by depositing a SiNx/AlOx 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 ρc with B, a good passivation with Ga, their degree of activation inside the poly‐Si and Si layers, and the annealing effects.