Charge Transfer in c-Si(n⁺⁺)/TiO₂(ALD) at the Amorphous/Anatase Transition: A Transient Surface Photovoltage...

Electronic properties and charge transfer processes were studied in an n-Si(n⁺⁺)/TiO₂(ALD) system at an amorphous TiO₂/anatase transition by transient surface photovoltage spectroscopy at constant photon flux. The TiO₂ layers were deposited by atomic layer deposition (ALD) onto highly doped silicon (c-Si(n⁺⁺)), and the phase composition of the TiO₂ layers changed with increasing thickness from amorphous to the anatase polymorph as anatase crystallites started to grow at the surface. Depending on phase composition, the band gap of TiO₂ correlated with the characteristic energy of exponential tails. In most cases, photogenerated electrons were separated toward the back contact. For photogeneration in c-Si(n⁺⁺), electron back transfer was limited by Auger recombination with holes in the surface space charge region of c-Si(n⁺⁺), and by electron transfer across the interface, either via exponentially distributed states near the conduction band edge of amorphous TiO₂ or via distance-dependent recombination with holes trapped in anatase. For photogeneration in TiO₂, electron back transfer was limited by trapping in TiO₂. Under strong light absorption in amorphous TiO₂ with anatase crystallites on top, electrons were preferentially separated toward the TiO₂ surface.