Charge transfer in c-Si(n ++ ) / TiO 2 (ALD) at the amorphous / anatase transition: A transient surface photovoltage spectroscopy study.

Electronic properties and charge transfer processes were studied in the n-Si(n) / TiO(ALD) system at the amorphous TiO / anatase transition by transient surface photovoltage spectroscopy at constant photon flux. The TiO layers were deposited by atomic layer deposition (ALD) onto highly doped silicon (c-Si(n)) and the phase composition of the TiO 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 TiO correlated with the characteristic energy of exponential tails.In most cases, photogenerated electrons were separated towards 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 TiO or via distance--dependent recombination with holes trapped in anatase. For photogeneration in TiO, electron back transfer was limited by trapping in TiO. Under strong light absorption in amorphous TiO with anatase crystallites on top, electrons were preferentially separated towards the TiO surface.