Modeling Field-effect in Black Silicon and its Impact on Device Performance

Black silicon (b-Si) has improved the performance of solar cells and photodetectors due to the excellent optics and surface passivation achieved with atomic layer deposition (ALD) dielectric films. One major reason for the success is the strong field effect caused by the high density of fixed charges present in the dielectric. Depending on the device, the field effect can be utilized also in a more active role than for mere surface passivation, including the formation of floating and/or induced junctions in silicon devices. However, in order to utilize the field effect efficiently, a deeper understanding of the thin-film charge-induced electric field and its effects on charge carriers in b-Si is required. Here, we investigate the field effect in b-Si using the Silvaco Atlas semiconductor device simulator. By studying the electric field and charge-carrier profiles, we develop a model where the electrical properties of b-Si can be approximated with a planar surface, which significantly simplifies the device-level simulations. We validate the model by simulating the spectral response of a b-Si -induced junction photodiode achieving less than 1% difference compared with experimental device performance in a wide range of wavelengths. Finally, we apply the model to study how variation in surface recombination velocity affects the short-wavelength sensitivity and dynamic range in a b-Si photodiode.