Töfflinger, J.A.; Laades, A.; Korte, L.; Leendertz, C.; Montanez, L. M.; Stürzebecher, U.; Sperlich, H-P.; Rech, B.: PECVD-AlOx/SiNx passivation stacks on wet chemically oxidized silicon: Constant voltage stress investigations of charge dynamics and interface defect states. Solar Energy Materials and Solar Cells 135 (2015), p. 49–56
10.1016/j.solmat.2014.09.024
Abstract:
The negative charge formation, the charge-trapping mechanisms and the interface defect passivation of aluminum oxide/silicon nitride ({AlOx}/{SiNx}) stacks deposited by plasma-enhanced chemical vapor deposition on p-type crystalline silicon (c-Si) are investigated. Constant voltage stress ({CVS}) investigations combined with capacitance–voltage (C–V) hysteresis analysis indicate the influence of different thermal treatments on the negative charge formation and allow discerning between fixed and trapped charges in the {AlOx}/{SiNx} system. The thermal budget during {SiNx} deposition activates negatively charged traps. An annealing step leads to the formation of a stable, fixed negative charge and reduces the defect state density (Dit) at the c-Si/{AlOx} interface. A wet-chemical silicon oxidation ({SiOx}) of the c-Si surface reduces Dit even further, but introduces additional traps at the wet-chemical {SiOx}/{AlOx} interface. These traps lead to instabilities of the negative charge density and have a detrimental effect on the passivation quality. However, a firing step leads to the formation of a higher negative charge density due to charged traps. Combined with the enhanced chemical passivation, this results in a higher passivation quality than upon annealing. The trap-related negative charge upon firing is unstable due to electron detrapping. However, a positive {CVS} can recharge traps in the wet-chemical {SiOx}/{AlOx}/{SiNx} system negatively through electron injection from the c-Si.