Electrical Deactivation of Boron in p+-Polycrystalline Silicon/SiOx/Crystalline Silicon Passivating Contacts for Silicon Solar Cells

Passivating junctions, like hole-collecting p+-polycrystalline silicon/SiOx/crystalline silicon junctions, need a thermal treatment to activate their excellent passivation and contact properties. Aside from surface passivation and from contact resistance between poly-Si and the substrate, the sheet resistance within the poly-Si is another important parameter for solar cell design. We present electrical investigations of in situ boron-doped (deposited by low pressure chemical vapor deposition) and ion-implanted (intrinsically deposited and subsequently ion-implanted with boron) p⁺-poly-Si/SiO_x/c-Si stacks after annealing. We find electrical deactivation of boron after annealing which strongly depends on the total boron concentration and the subsequent annealing temperature.