Understanding field-effect passivation of black silicon: modeling charge carrier population control in compressed space charge regions

A considerable amount of literature has revealed the effectiveness of surface passivation by charge carrier population control either using dopant profiles or charged dielectrics. Most studies assume that the substrate thickness is far larger than the space charge region. However, this assumption does not hold for nano-structured surfaces such as black silicon. In this work, we use one-dimensional modeling to understand the effect of nano-features on charge carrier population control by dielectric fixed charge Q_f. We find that when Q_f is smaller than ∼1×10¹¹ cm⁻², the decreasing two-surface distance will effectively compress the space charge region and intensify the surface carrier asymmetry, which can be considered as an enhancement of charge carrier population control for surface passivation. Nevertheless, when the Q_f magnitude is larger than ∼1×10¹¹ cm⁻², the mirrored charge tends to concentrate at the near-surface region, and the space charge region compression is less effective. This leads to a reduced influence on the charge carrier population control and consequently little enhanced surface passivation.