Failure modes of protection layers produced by atomic layer deposition of amorphous TiO₂ on GaAs anodes

Abstract

Amorphous titanium dioxide (a-TiO2) films formed by atomic layer deposition can serve as protective coatings for semiconducting photoanodes in water-splitting cells using strongly alkaline aqueous electrolytes. Herein, we experimentally examine...

Understanding the Stability of Etched or Platinized p-GaInP Photocathodes for Solar-Driven H2 Evolution

“…Alloys of the III–V elements provide a proven approach to tuning the band gap of the semiconducting materials. For instance, ternary compounds of GaInP, GaAsP, and AlGaAs can all exhibit the desired band gap of 1.8 eV. , However, many III–V semiconductors, such as InP and GaAs, suffer from anodic photocorrosion under potentials sufficient to drive the OER. − The cathodic stability of most III–V semiconductors, especially under HER conditions at pH 0 or pH 14, is not however yet fully defined. Under HER conditions, p-GaAs surfaces form excess elemental As, leading to a loss of electrode photoactivity .…”

GaAs Microisland Anodes Protected by Amorphous TiO2 Films Mitigate Corrosion Spreading During Water Oxidation in Alkaline Electrolytes

“…9,10 Planar p + -GaAs samples that had been coated with a-TiO 2 films grown under these conditions (TDMAT, 150 °C) with minimal pinholes from atmospheric particulate contamination develop defect sites after ∼10 h of electrochemical operation. 8 Defective regions that exhibit behavior in accord with expectations for small domains of a metastable crystalline phase of TiO 2 9,10 thus presumably exist in the film even though no crystalline regions were detected using Raman spectroscopy.…”

“…12 Galvanic deposition of Au allows for the staining of pinholes in a-TiO 2 films on GaAs and indicates that pinhole densities in the a-TiO 2 films can readily be reduced to below 1 defect per 10 −3 cm 2 even if the a-TiO 2 films are deposited under an ambient atmosphere in the laboratory. 8 Consequently, we describe herein the use of ∼200 μm diameter circular islands of TiO 2 -protected GaAs anodes to demonstrate the benefits of spatially isolating extrinsic defects in protected semiconductor electrodes that undergo pit corrosion as well as to further define and understand the short-and midterm failure Crystallinity of a-TiO 2 . Figure S1 shows a representative Raman spectrum of a GaAs sample coated with 2000 cycles of a-TiO 2 (GaAs/2000×-a-TiO 2 ) from tetrakis(dimethylamido)titanium (TDMAT) as the Ti source.…”

Investigation of n-GaAs Photoanode Corrosion in Acidic Media with Various Thin Ir Cocatalyst Layers

“…Electroless deposition via galvanic displacement of metals onto a semiconductor surface is a simple, cost-effective, high-throughput method for thin layers that has routinely been employed to produce metal–semiconductor contacts. Reports of galvanic displacement of noble metals on n-GaAs have shown the formation of thin films of Au, Ag, and Pt. − The promise of this method for conformal surface coverage is highlighted by a recent report using electroless deposition of gold on amorphous-TiO 2 protected p + -GaAs electrodes as a failure detection method for the protection layer by imaging Au deposits in the pinholes . However, Ir oxide is one of the only highly active OER catalysts which is stable under anodic potentials in strongly acidic media .…”

“…30−32 The promise of this method for conformal surface coverage is highlighted by a recent report using electroless deposition of gold on amorphous-TiO 2 protected p + -GaAs electrodes as a failure detection method for the protection layer by imaging Au deposits in the pinholes. 33 However, Ir oxide is one of the only highly active OER catalysts which is stable under anodic potentials in strongly acidic media. 34 According to the reduction potentials of different noble metal anions with respect to the valence band of GaAs, Ir can be deposited from hexachloroiridate salts onto n-GaAs by galvanic displacement.…”