Silicon surface passivation by atomic layer deposited Al2O3

Thin Al2O3 films with a thickness of 7-30 nm synthesized by plasma-assisted at. layer deposition (ALD) were used for surface passivation of cryst. silicon (c-Si) of different doping concns. The level of surface passivation in this study was detd. by techniques based on photoconductance, photoluminescence, and IR emission. Effective surface recombination velocities of 2 and 6 cm/s were obtained on 1.9 W cm n-type and 2.0 W cm p-type c-Si, resp. An effective surface recombination velocity below 1 cm/s was unambiguously obtained for nearly intrinsic c-Si passivated by Al2O3. A high d. of neg. fixed charges was detected in the Al2O3 films and its impact on the level of surface passivation was demonstrated exptl. The neg. fixed charge d. results in a flat injection level dependence of the effective lifetime on p-type c-Si and explains the excellent passivation of highly B-doped c-Si by Al2O3. Furthermore, a brief comparison is presented between the surface passivations achieved for thermal and plasma-assisted ALD Al2O3 films prepd. in the same ALD reactor