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Microscopic Study of Atomic Layer Deposition of TiO2on GaAs and Its Photocatalytic Application

  • Author(s): Qiu, J
  • Zeng, G
  • Ha, MA
  • Hou, B
  • Mecklenburg, M
  • Shi, H
  • Alexandrova, AN
  • Cronin, SB
  • et al.
Abstract

© 2015 American Chemical Society. We report a microscopic study of p-GaAs/TiO2heterojunctions using cross-sectional high resolution transmission electron microscopy (HRTEM). The photocatalytic performance for both H2evolution and CO2reduction of these heterostructures shows a very strong dependence on the thickness of the TiO2over the range of 0-15 nm. Thinner films (1-10 nm) are amorphous and show enhanced catalytic performance with respect to bare GaAs. HRTEM images and electron energy loss spectroscopy (EELS) maps show that the native oxide of GaAs is removed by the TiCl4atomic layer deposition (ALD) precursor, which is corrosive. Ti3+defect states (i.e., O vacancies) in the TiO2film provide catalytically active sites, which improve the photocatalytic efficiency. Density functional theory (DFT) calculations show that water molecules and CO2molecules bind stably to these Ti3+states. Thicker TiO2films (15 nm) are crystalline and have poor charge transfer due to their insulating nature, while thinner amorphous TiO2films are conducting.

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