Corona charging and optical second-harmonic generation studies of the field-effect passivation of c-SI by Al2O3 films

Aluminum oxide films (Al₂O₃) synthesized by atomic layer deposition (ALD) provide an excellent level of surface passivation of n^-, p^-, and heavily doped p-type crystalline silicon (c-Si). It has been shown that a negative fixed charge density in the order of 10¹²-10¹³ cm^-2 can be present at the interface of Al₂O₃ with c-Si, inducing a high level of field-effect passivation. In this contribution we report on results obtained by two complementary, contactless techniques to investigate the field-effect passivation for the Al₂O₃/c-Si case: optical second-harmonic generation (SHG) and corona charging. From an extensive data set on Al₂O₃ thin films, we demonstrate that the combination of SHG and corona charging offers the advantage of probing the presence of fixed charges at the interface non-intrusively (SHG) and of extracting the fixed charge density quantitatively (corona). These two techniques are therefore powerful tools for investigating the mechanisms responsible for the passivation properties of thin films.