Field-Effect Passivation of Undiffused Black Silicon Surfaces

Black silicon (b-Si) surfaces typically have a high density of extreme nanofeatures and a significantly large surface area. This makes high-quality surface passivation even more critical for devices such as solar cells with b-Si surfaces. It has been hypothesized that conformal dielectrics with a high fixed charge density (Q(f)) are preferred as the nanoscale features of b-Si result in a significant enhancement of field-effect passivation. This article uses 1-D, 2-D, and 3-D numerical simulations to study surface passivation of b-Si, where we particularly focus on the charge carrier control by vertical bar Q(f)vertical bar up to 1 x 10(13) cm(-2) under accumulation conditions. We will show that there is a significant space charge region compression in b-Si nanofeatures, which affects the charge carrier population control formoderate vertical bar Q(f)vertical bar up to approximate to 1x10(12) cm(-2). The average surfaceminority charge carrier density can be reduced by 70% in some cases, resulting in an equivalent reduction in area-normalized surface recombination losses if the effective surface recombination velocity (S-eff) is limited by minority carriers. This provides a possible solution for the empirical S-eff proportional to 1/Q(f)(4) reported previously. We will also show that the situation is more complicated for surface passivation films where the ratio between the electron and hole capture cross section (sigma(n)/sigma(p)) is higher than 10 for p-type surfaces. For commonly used surface passivation films with a vertical bar Q(f)vertical bar larger than approximate to 1 x 10(12) cm(-2), there is little space charge compression for b-Si. Consequently, S-eff simply scales with the surface area, i.e., there is no enhanced reduction of surface recombination by field-effect passivation on b-Si.

Automated summary

The study focuses on the surface passivation of black silicon (b-Si) and control of charge carriers in nanofeatures of b-Si surfaces. Compression of space charge region is found in b-Si nanofeatures, leading to reduction in surface minority charge carrier density and surface recombination losses. The behavior of surface passivation films is complex, with little space charge compression for b-Si with high fixed charge density, indicating that enhanced reduction of surface recombination by field-effect passivation may not occur.