Electronic Band Offset Determination of Oxides Grown by Atomic Layer Deposition on Silicon

Minimizing electrical losses at metal/silicon interfaces in high-efficiency single-junction silicon solar cells requires the use of carrier-selective passivating contacts. The electronic barrier heights at the insulator/silicon interface are necessary for calculating the probability of quantum tunneling of charge carriers at these interfaces. Thus, precise knowledge of these parameters is crucial for the development of contact schemes. Using a photoemission-based method, we experimentally determine the electronic band offsets of Al2O3, HfO2and SiO2layers grown by atomic layer deposition (ALD) on silicon. For Al2O3/Si, we determine a valence band offset (ΔEV) and conduction band offset (ΔEC) of 3.29 ± 0.07 eV and 2.24 ± 0.13 eV, respectively. For HfO2/Si, ΔEVand ΔECare determined as 2.67 ± 0.07 eV and 1.81 ± 0.21 eV, while for SiO2/Si, ΔEVand ΔECare 4.87 ± 0.07 eV and 2.61 ± 0.12 eV, respectively. Using technology computer-aided design simulations, we incorporate our experimental results to estimate the contact resistivity that would be attained at various dielectric layer thicknesses. We find that for achieving the 100 mΩ·cm2contact resistivity benchmark, Al2O3layers should be no thicker than 1.65 nm for ap-type polysilicon-based hole-selective contact, assuming hole tunneling masses taken from the literature. Correspondingly, for HfO2and SiO2, an upper limit of 1.4 nm is determined as the thickness threshold in order to utilize these ALD-grown layers for contacts in high-performance silicon photovoltaics.