Enhanced field effect passivation of c-Si surface via introduction of trap centers: Case of hafnium and aluminium oxide bilayer films deposited by thermal ALD

Field effect passivation of crystalline silicon surface is controlled by tailoring the built-in charge in a bilayer dielectric system consisting of hafnium oxide (HfO2) and aluminium oxide (Al2O3). The effective surface recombination velocity (Seff, max) ~ 10 cm/s is achieved at intermediate bulk injection levels with thermal ALD deposited HfO2 (top)/Al2O3 (bottom) bilayer system on n-type silicon with individual layer thickness between 3 and 7 nm. The best realized Seff,max value is lower by a factor of ~ 2.5 with respect to the single Al2O3 layer of similar thickness deposited under the same experimental conditions. The improved field effect passivation is quantified by enhanced effective charge density for the bilayer system in comparison with the corresponding value for single Al2O3 layer. The introduction of extra trap centers at the interface of the bilayer system is primarily responsible for the enriched field effect passivation, however, the sequence of the dielectric layers is important.