Jan-Dirk Kähler

Dopant diffusion from p + -poly-Si into c-Si during thermal annealing

Passivating junctions, like hole-collecting p-polycrystalline silicon/SiOx/crystalline silicon junctions, need a thermal activation to activate their excellent passivation and contact properties. Here, the diffusion of boron from the highly doped poly-Si layer into the Si is often considered to compromise the passivation quality. In contrast we show that at least a slight diffusion of boron into the crystalline silicon is present for optimized annealing conditions. We achieve low emitter saturation current densities of 11 fA/cm2 for in situ p+ doped polysilicon deposited by low pressure chemical vapor deposition. Furthermore, we show that the polysilicon layer and the in- diffused region within the substrate are electrically connected.

Evolution of oxide disruptions: The (W)hole story about poly-Si/c-Si passivating contacts

Different models exist describing the current transport in polycrystalline Si/SiOx/crystalline Si junctions. Besides tunneling through thin oxides, transport through pinholes is discussed. We investigate the influence of annealing temperature on the structural properties of polycrystalline Si/SiOx/crystalline Si interfaces and analyze the formation and evolution of holes by high resolution transmission electron microscopy in comparison to electrical results. We prove the existence of pinholes in samples with good electrical properties in agreement with the pinhole model.

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/SiOx/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.