Surface Passivation by Atomic-layer-deposited Al2O3/TiO2 Stacks

A detailed study of the passivation quality of Al2O3 and TiO2 stacks on boron-doped emitters, where the stacks were deposited by thermal atomic layer deposition. The passivation quality was studied for different post-TiO2 anneal temperature, as a function of Al2O3 and TiO2 layer thickness. For annealed Al2O3 layers, as-deposited TiO2 capping layer decreased emitter saturation current density considerably, which was more significant on Al2O3 with thickness below 10 nm. However, post-TiO2 deposition anneal in O-2 environment degraded the passivation, which was attributed to the increasing interface trap density in spite of increasing effective fixed charge density.